Commit graph

72 commits

Author SHA1 Message Date
Emilio G. Cota 8552d95c52
exec-all: extract tb->tc_* into a separate struct tc_tb
In preparation for adding tc.size to be able to keep track of
TB's using the binary search tree implementation from glib.

Backports commit e7e168f41364c6e83d0f75fc1b3ce7f9c41ccf76 from qemu
2018-03-05 02:57:22 -05:00
Emilio G. Cota 5fc83f3eb2
exec-all: introduce TB_PAGE_ADDR_FMT
And fix the following warning when DEBUG_TB_INVALIDATE is enabled
in translate-all.c:

CC mipsn32-linux-user/accel/tcg/translate-all.o
/data/src/qemu/accel/tcg/translate-all.c: In function ‘tb_alloc_page’:
/data/src/qemu/accel/tcg/translate-all.c:1201:16: error: format ‘%lx’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘tb_page_addr_t {aka unsigned int}’ [-Werror=format=]
printf("protecting code page: 0x" TARGET_FMT_lx "\n",
^
cc1: all warnings being treated as errors
/data/src/qemu/rules.mak:66: recipe for target 'accel/tcg/translate-all.o' failed
make[1]: *** [accel/tcg/translate-all.o] Error 1
Makefile:328: recipe for target 'subdir-mipsn32-linux-user' failed
make: *** [subdir-mipsn32-linux-user] Error 2
cota@flamenco:/data/src/qemu/build ((18f3fe1...) *$)$

Backports commit 67a5b5d2f6eb6d3b980570223ba5c478487ddb6f from qemu
2018-03-05 02:49:44 -05:00
Emilio G. Cota b4a7d8b773
exec-all: bring tb->invalid into tb->cflags
This gets rid of a hole in struct TranslationBlock.

Backports commit 84f1c148da2b35fbb5a436597872765257e8914e from qemu
2018-03-05 02:46:21 -05:00
Emilio G. Cota 68ddc0cb08
exec-all: fix typos in TranslationBlock's documentation
Backports commit eb5e2b9e3b141de0c435eedc31c26cbbdefbee1b from qemu
2018-03-05 02:10:28 -05:00
Richard Henderson 31b8b67cd3
tcg: Move USE_DIRECT_JUMP discriminator to tcg/cpu/tcg-target.h
Replace the USE_DIRECT_JUMP ifdef with a TCG_TARGET_HAS_direct_jump
boolean test. Replace the tb_set_jmp_target1 ifdef with an unconditional
function tb_target_set_jmp_target.

While we're touching all backends, add a parameter for tb->tc_ptr;
we're going to need it shortly for some backends.

Move tb_set_jmp_target and tb_add_jump from exec-all.h to cpu-exec.c.

Backports commit a85833933628384d74ec412024d55cf012640287 from qemu
2018-03-04 21:52:35 -05:00
Lluís Vilanova 3a196c62ae
target: [tcg] Use a generic enum for DISAS_ values
Used later. An enum makes expected values explicit and
bounds the value space of switches.

Backports commit 77fc6f5e28667634916f114ae04c6029cd7b9c45 from qemu
2018-03-04 14:08:43 -05:00
Richard Henderson b8a16f841a
tcg: Add generic DISAS_NORETURN
This will allow some amount of cleanup to happen before
switching the backends over to enum DisasJumpType.

Backports commit 5dc66895b0113034cd37fd5e65911d7959fc26a9 from qemu
2018-03-04 13:49:18 -05:00
Lluís Vilanova 32b3c3815d
tcg: Pass generic CPUState to gen_intermediate_code()
Needed to implement a target-agnostic gen_intermediate_code()
in the future.

Backports commit 9c489ea6bed134fecfd556b439c68bba48fbe102 from qemu
2018-03-03 23:34:18 -05:00
Alex Bennée 7d02489baf
include/exec/exec-all: document common exit conditions
As a precursor to later patches attempt to come up with a more
concrete wording for what each of the common exit cases would be.

Backports commit df0311e634828fdc99ca59352aef68503d631aad from qemu
2018-03-03 22:31:28 -05:00
Pranith Kumar d0a70720a3
Revert "exec.c: Fix breakpoint invalidation race"
Now that we have proper locking after MTTCG patches have landed, we
can revert the commit. This reverts commit

a9353fe897ca2687e5b3385ed39e3db3927a90e0.

Backports commit 406bc339b0505fcfc2ffcbca1f05a3756e338a65 from qemu
2018-03-03 22:14:35 -05:00
Yang Zhong 1135db176f
tcg: add CONFIG_TCG guards in headers
Add CONFIG_TCG around TLB-related functions and structure declarations.
Some of these functions are defined in ./accel/tcg/cputlb.c, which will
not be linked in if TCG is disabled, and have no stubs; therefore, their
callers will also be compiled out for --disable-tcg.

Backports commit b11ec7f2e44b285a3967d629b55d1a6970b06787 from qemu
2018-03-03 21:37:52 -05:00
Yang Zhong d70c141675
tcg: move page_size_init() function
translate-all.c will be disabled if tcg is disabled in the build,
so page_size_init() function and related variables will be moved
to exec.c file.

Backports commit a0be0c585f5dcc4d50a37f6a20d3d625c5ef3a2c from qemu
2018-03-03 21:30:08 -05:00
Richard Henderson 68275ba6f3
tcg/arm: Use indirect branch for goto_tb
Backports commit 3fb53fb4d12f2e7833bd1659e6013237b130ef20 from qemu
2018-03-03 17:11:18 -05:00
Emilio G. Cota 8f4f15e5f5
tcg: Introduce goto_ptr opcode and tcg_gen_lookup_and_goto_ptr
Instead of exporting goto_ptr directly to TCG frontends, export
tcg_gen_lookup_and_goto_ptr(), which calls goto_ptr with the pointer
returned by the lookup_tb_ptr() helper. This is the only use case
we have for goto_ptr and lookup_tb_ptr, so having this function is
very convenient. Furthermore, it trivially allows us to avoid calling
the lookup helper if goto_ptr is not implemented by the backend.

Backports commit cedbcb01529cb6cf9a2289cdbebbc63f6149fc18 from qemu
2018-03-02 21:05:18 -05:00
Alex Bennée 454932263c
cputlb and arm/sparc targets: convert mmuidx flushes from varg to bitmap
While the vargs approach was flexible the original MTTCG ended up
having munge the bits to a bitmap so the data could be used in
deferred work helpers. Instead of hiding that in cputlb we push the
change to the API to make it take a bitmap of MMU indexes instead.

For ARM some the resulting flushes end up being quite long so to aid
readability I've tended to move the index shifting to a new line so
all the bits being or-ed together line up nicely, for example:

tlb_flush_page_by_mmuidx(other_cs, pageaddr,
(1 << ARMMMUIdx_S1SE1) |
(1 << ARMMMUIdx_S1SE0));

Backports commit 0336cbf8532935d8e23c2aabf3e2ce2c0697b6ac from qemu
2018-03-02 10:12:40 -05:00
Alex Bennée e3e57ca08e
cputlb: drop flush_global flag from tlb_flush
We have never has the concept of global TLB entries which would avoid
the flush so we never actually use this flag. Drop it and make clear
that tlb_flush is the sledge-hammer it has always been.

Backports commit  d10eb08f5d8389c814b554d01aa2882ac58221bf from qemu
2018-03-01 19:36:04 -05:00
Paolo Bonzini 9404dbf74e
cpu-exec: fix icount out-of-bounds access
When icount is active, tb_add_jump is surprisingly called with an
out of bounds basic block index. I have no idea how that can work,
but it does not seem like a good idea. Clear *last_tb for all
TB_EXIT_ICOUNT_EXPIRED cases, even when all you have to do is
refill icount_extra.

Backports commit d8dea6fbcbed177ca5d23ab77b3834a9437f0e88 from qemu
2018-03-01 09:17:26 -05:00
Paolo Bonzini 9d64a89acf
tcg: comment on which functions have to be called with tb_lock held
softmmu requires more functions to be thread-safe, because translation
blocks can be invalidated from e.g. notdirty callbacks. Probably the
same holds for user-mode emulation, it's just that no one has ever
tried to produce a coherent locking there.

This patch will guide the introduction of more tb_lock and tb_unlock
calls for system emulation.

Note that after this patch some (most) of the mentioned functions are
still called outside tb_lock/tb_unlock. The next one will rectify this.

Backports commit 7d7500d99895f888f97397ef32bb536bb0df3b74 from qemu
2018-02-28 10:26:28 -05:00
Alex Bennée 7aab0bd9a6
translate-all: add DEBUG_LOCKING asserts
This adds asserts to check the locking on the various translation
engines structures. There are two sets of structures that are protected
by locks.

The first the l1map and PageDesc structures used to track which
translation blocks are associated with which physical addresses. In
user-mode this is covered by the mmap_lock.

The second case are TB context related structures which are protected by
tb_lock which is also user-mode only.

Currently the asserts do nothing in SoftMMU mode but this will change
for MTTCG.

Backports commit 301e40ed8005306c009978be295ed9a4b725178b from qemu
2018-02-28 08:56:15 -05:00
Yongbok Kim 79e4c001a9
softmmu: Add probe_write()
Probe for whether the specified guest write access is permitted.
If it is not permitted then an exception will be taken in the same
way as if this were a real write access (and we will not return).
Otherwise the function will return, and there will be a valid
entry in the TLB for this access.

Backports commit 3b4afc9e75ab1a95f33e41f462921093f8a109c4 from qemu
2018-02-27 12:20:50 -05:00
Richard Henderson e35aacd5ae
tcg: Add EXCP_ATOMIC
When we cannot emulate an atomic operation within a parallel
context, this exception allows us to stop the world and try
again in a serial context.

Backports commit fdbc2b5722f6092e47181a947c90fd4bdcc1c121 from qemu

Also backports parts of commit 02d57ea115b7669f588371c86484a2e8ebc369be
2018-02-27 11:57:58 -05:00
Richard Henderson 66d79ac959
tcg: Merge GETPC and GETRA
The return address argument to the softmmu template helpers was
confused. In the legacy case, we wanted to indicate that there
is no return address, and so passed in NULL. However, we then
immediately subtracted GETPC_ADJ from NULL, resulting in a non-zero
value, indicating the presence of an (invalid) return address.

Push the GETPC_ADJ subtraction down to the only point it's required:
immediately before use within cpu_restore_state_from_tb, after all
NULL pointer checks have been completed.

This makes GETPC and GETRA identical. Remove GETRA as the lesser
used macro, replacing all uses with GETPC.

Backports commit 01ecaf438b1eb46abe23392c8ce5b7628b0c8cf5 from qemu
2018-02-26 02:54:44 -05:00
Paolo Bonzini 30845ae475
tcg: Prepare TB invalidation for lockless TB lookup
When invalidating a translation block, set an invalid flag into the
TranslationBlock structure first. It is also necessary to check whether
the target TB is still valid after acquiring 'tb_lock' but before calling
tb_add_jump() since TB lookup is to be performed out of 'tb_lock' in
future. Note that we don't have to check 'last_tb'; an already invalidated
TB will not be executed anyway and it is thus safe to patch it.

Backports commit 6d21e4208f382dd8ca1f7995a6dd9ea7ca281163 from qemu
2018-02-26 01:48:13 -05:00
Igor Mammedov 62c89b9cd4
exec: Reduce CONFIG_USER_ONLY ifdeffenery
Backports commit 1bc7e522d9cf1b58f2de9c8f1737be0bb5129c35 from qemu
2018-02-25 20:57:48 -05:00
Markus Armbruster 1275b9b459
Clean up ill-advised or unusual header guards
Cleaned up with scripts/clean-header-guards.pl.

Backports commit 2a6a4076e117113ebec97b1821071afccfdfbc96 from qemu
2018-02-25 04:22:46 -05:00
Sergey Sorokin d1e4ac0451
Fix confusing argument names in some common functions
There are functions tlb_fill(), cpu_unaligned_access() and
do_unaligned_access() that are called with access type and mmu index
arguments. But these arguments are named 'is_write' and 'is_user' in their
declarations. The patches fix the arguments to avoid a confusion.

Backports commit b35399bb4e9968296a12303b00f9f2066470e987 from qemu
2018-02-25 03:58:27 -05:00
Peter Maydell d7dccff836
cpu-exec: Rename cpu_resume_from_signal() to cpu_loop_exit_noexc()
The function cpu_resume_from_signal() is now always called with a
NULL puc argument, and is rather misnamed since it is never called
from a signal handler. It is essentially forcing an exit to the
top level cpu loop but without raising any exception, so rename
it to cpu_loop_exit_noexc() and drop the useless unused argument.

Backports commit 6886b98036a8f8f5bce8b10756ce080084cef11b from qemu
2018-02-24 17:25:28 -05:00
Paolo Bonzini 9485b7c2e1
cpu: move exec-all.h inclusion out of cpu.h
exec-all.h contains TCG-specific definitions. It is not needed outside
TCG-specific files such as translate.c, exec.c or *helper.c.

One generic function had snuck into include/exec/exec-all.h; move it to
include/qom/cpu.h.

Backports commit 63c915526d6a54a95919ebece83fa9ca631b2508 from qemu
2018-02-24 02:39:08 -05:00
Paolo Bonzini 58693409ea
exec: extract exec/tb-context.h
TCG backends do not need most of exec-all.h; extract what they actually
need to a separate file or move it directly to tcg.h. The next patch
will stop including exec-all.h from everywhere.

Backports commit 00f6da6a1a5d1ce085334eccbb50ec899ceed513 from qemu
2018-02-24 02:09:58 -05:00
Sergey Fedorov ba9a237586
tcg: Rework tb_invalidated_flag
'tb_invalidated_flag' was meant to catch two events:
* some TB has been invalidated by tb_phys_invalidate();
* the whole translation buffer has been flushed by tb_flush().

Then it was checked:
* in cpu_exec() to ensure that the last executed TB can be safely
linked to directly call the next one;
* in cpu_exec_nocache() to decide if the original TB should be provided
for further possible invalidation along with the temporarily
generated TB.

It is always safe to patch an invalidated TB since it is not going to be
used anyway. It is also safe to call tb_phys_invalidate() for an already
invalidated TB. Thus, setting this flag in tb_phys_invalidate() is
simply unnecessary. Moreover, it can prevent from pretty proper linking
of TBs, if any arbitrary TB has been invalidated. So just don't touch it
in tb_phys_invalidate().

If this flag is only used to catch whether tb_flush() has been called
then rename it to 'tb_flushed'. Declare it as 'bool' and stick to using
only 'true' and 'false' to set its value. Also, instead of setting it in
tb_gen_code(), just after tb_flush() has been called, do it right inside
of tb_flush().

In cpu_exec(), this flag is used to track if tb_flush() has been called
and have made 'next_tb' (a reference to the last executed TB) invalid
for linking it to directly call the next TB. tb_flush() can be called
during the CPU execution loop from tb_gen_code(), during TB execution or
by another thread while 'tb_lock' is released. Catch for translation
buffer flush reliably by resetting this flag once before first TB lookup
and each time we find it set before trying to add a direct jump. Don't
touch in in tb_find_physical().

Each vCPU has its own execution loop in multithreaded mode and thus
should have its own copy of the flag to be able to reset it with its own
'next_tb' and don't affect any other vCPU execution thread. So make this
flag per-vCPU and move it to CPUState.

In cpu_exec_nocache(), we only need to check if tb_flush() has been
called from tb_gen_code() called by cpu_exec_nocache() itself. To do
this reliably, preserve the old value of the flag, reset it before
calling tb_gen_code(), check afterwards, and combine the saved value
back to the flag.

This patch is based on the patch "tcg: move tb_invalidated_flag to
CPUState" from Paolo Bonzini <pbonzini@redhat.com>.

Backports commit 6f789be56d3f38e9214dafcfab3bf9be7191f370 from qemu
2018-02-23 23:34:51 -05:00
Sergey Fedorov d60af028c5
tcg: Clarify thread safety check in tb_add_jump()
The check is to make sure that another thread hasn't already done the
same while we were outside of tb_lock. Mention this in a comment.

Backports commit 9962c478b153a18fe88a6509fe58cd178aff8abc from qemu
2018-02-23 21:32:47 -05:00
Sergey Fedorov fbc0a1105f
tcg: Use uintptr_t type for jmp_list_{next|first} fields of TB
These fields do not contain pure pointers to a TranslationBlock
structure. So uintptr_t is the most appropriate type for them.
Also put some asserts to assure that the two least significant bits of
the pointer are always zero before assigning it to jmp_list_first.

Backports commit c37e6d7e3589ecb96914faa21025ad7ba6654aea from qemu
2018-02-23 21:28:19 -05:00
Sergey Fedorov e60c24cecf
tcg: Clean up direct block chaining data fields
Briefly describe in a comment how direct block chaining is done. It
should help in understanding of the following data fields.

Rename some fields in TranslationBlock and TCGContext structures to
better reflect their purpose (dropping excessive 'tb_' prefix in
TranslationBlock but keeping it in TCGContext):
tb_next_offset => jmp_reset_offset
tb_jmp_offset => jmp_insn_offset
tb_next => jmp_target_addr
jmp_next => jmp_list_next
jmp_first => jmp_list_first

Avoid using a magic constant as an invalid offset which is used to
indicate that there's no n-th jump generated.

Backports commit f309101c26b59641fc1aa8fb2a98a5441cdaea03 from qemu
2018-02-23 21:28:19 -05:00
Sergey Fedorov c5b234ed1f
tcg: Note requirement on atomic direct jump patching
Backports commit 10b4f4855537dd421e193a7d0416513116370558 from qemu
2018-02-23 21:28:18 -05:00
Sergey Fedorov 52e2972300
tcg/arm: Make direct jump patching thread-safe
Ensure direct jump patching in ARM is atomic by using
atomic_read()/atomic_set() for code patching.

Backports commit 7d14e0e2d661479985197203589c38840e1066df from qemu
2018-02-23 21:28:18 -05:00
Sergey Fedorov 57359fbe6c
tcg/s390: Make direct jump patching thread-safe
Ensure direct jump patching in s390 is atomic by:
* naturally aligning a location of direct jump address;
* using atomic_read()/atomic_set() for code patching.

Backports commit ed3d51ecd7fe248d3959e469d53890ac9ffe0cd2 from qemu
2018-02-23 21:28:18 -05:00
Sergey Fedorov 5eb2d6618f
tcg/i386: Make direct jump patching thread-safe
Ensure direct jump patching in i386 is atomic by:
* naturally aligning a location of direct jump address;
* using atomic_read()/atomic_set() for code patching.

Backports commit 0d07abf05e98903c7faf204a9a90f7d45b7554dc from qemu
2018-02-23 21:28:17 -05:00
Emilio G. Cota 170f6e0b3b
tb: consistently use uint32_t for tb->flags
We are inconsistent with the type of tb->flags: usage varies loosely
between int and uint64_t. Settle to uint32_t everywhere, which is
superior to both: at least one target (aarch64) uses the most significant
bit in the u32, and uint64_t is wasteful.

Compile-tested for all targets.

Backports commit 89fee74a0f066dfd73830a7b5fa137e87888c870 from qemu
2018-02-23 21:28:11 -05:00
Lioncash 87130fc884
exec-all: Remove externs
These are unused
2018-02-23 12:43:03 -05:00
Peter Crosthwaite 576f1752a6
include/exec: Move cputlb exec.c defs out
Move the architecture agnostic function prototypes for exec.c out of
cputlb.h to exec-all.h. This allows hiding of the arch specific
cputlb.h from exec.c which should be getting close to having no
architecture specifics. Prepares support for multi-arch, which will have
a minimal cpu.h that services exec.c but not cputlb.h.

Backports commit dfccc7602374c9fd3b083208b552d62daa244811 from qemu
2018-02-23 10:52:25 -05:00
Alex Bennée 3da7d9d9ae
qemu-log: dfilter-ise exec, out_asm, op and opt_op
qemu-log: dfilter-ise exec, out_asm, op and opt_op

This ensures the code generation debug code will honour -dfilter if set.
For the "exec" tracing I've added a new inline macro for efficiency's
sake.

Backports commit d977e1c2dbc9e63454b2000f91954d02543bf43b from qemu
2018-02-22 10:06:19 -05:00
Peter Maydell 3f5e36e15f
qemu-log: Improve the exec TB execution logging
Improve the TB execution logging so that it is easier to identify
what is happening from trace logs:
* move the "Trace" logging of executed TBs into cpu_tb_exec()
so that it is emitted if and only if we actually execute a TB,
and for consistency for the CPU state logging
* log when we link two TBs together via tb_add_jump()
* log when cpu_tb_exec() returns early from a chain of TBs

The new style logging looks like this:

Trace 0x7fb7cc822ca0 [ffffffc0000dce00]
Linking TBs 0x7fb7cc822ca0 [ffffffc0000dce00] index 0 -> 0x7fb7cc823110 [ffffffc0000dce10]
Trace 0x7fb7cc823110 [ffffffc0000dce10]
Trace 0x7fb7cc823420 [ffffffc000302688]
Trace 0x7fb7cc8234a0 [ffffffc000302698]
Trace 0x7fb7cc823520 [ffffffc0003026a4]
Trace 0x7fb7cc823560 [ffffffc0000dce44]
Linking TBs 0x7fb7cc823560 [ffffffc0000dce44] index 1 -> 0x7fb7cc8235d0 [ffffffc0000dce70]
Trace 0x7fb7cc8235d0 [ffffffc0000dce70]
Stopped execution of TB chain before 0x7fb7cc8235d0 [ffffffc0000dce70]
Trace 0x7fb7cc8235d0 [ffffffc0000dce70]
Trace 0x7fb7cc822fd0 [ffffffc0000dd52c]

Backports commit 1a830635229e14c403600167823ea6b3b79d3097 from qemu
2018-02-22 09:40:11 -05:00
Lioncash 6d5f465449
uc: Handle freeing of multiple address spaces 2018-02-18 21:36:50 -05:00
Peter Maydell 1dfba71bef
exec.c: Add cpu_get_address_space()
Add a function to return the AddressSpace for a CPU based on
its numerical index. (Callers outside exec.c don't have access
to the CPUAddressSpace struct so can't just fish it out of the
CPUState struct directly.)

Backports commit 651a5bc03705102de519ebf079a40ecc1da991db from qemu
2018-02-17 23:22:23 -05:00
Peter Maydell 2fe995a0da
exec.c: Pass MemTxAttrs to iotlb_to_region so it uses the right AS
Pass the MemTxAttrs for the memory access to iotlb_to_region(); this
allows it to determine the correct AddressSpace to use for the lookup.

Backports commit a54c87b68a0410d0cf6f8b84e42074a5cf463732 from qemu
2018-02-17 23:19:00 -05:00
Peter Maydell 8edd6ffdfd
cputlb.c: Use correct address space when looking up MemoryRegionSection
When looking up the MemoryRegionSection for the new TLB entry in
tlb_set_page_with_attrs(), use cpu_asidx_from_attrs() to determine
the correct address space index for the lookup, and pass it into
address_space_translate_for_iotlb().

Backports commit d7898cda81b6efa6b2d7a749882695cdcf280eaa from qemu
2018-02-17 23:15:22 -05:00
Peter Maydell 90c7c1bdb5
exec-all.h: Document tlb_set_page_with_attrs, tlb_set_page
Add documentation comments for tlb_set_page_with_attrs()
and tlb_set_page().

Backports commit 1787cc8ee55143b6071c87e59f08d56e7c22c1eb from qemu
2018-02-17 22:37:58 -05:00
Peter Maydell 51369b67cd
exec.c: Allow target CPUs to define multiple AddressSpaces
Allow multiple calls to cpu_address_space_init(); each
call adds an entry to the cpu->ases array at the specified
index. It is up to the target-specific CPU code to actually use
these extra address spaces.

Since this multiple AddressSpace support won't work with
KVM, add an assertion to avoid confusing failures.

Backports commit 12ebc9a76dd7702aef0a3618717a826c19c34ef4 from qemu
2018-02-17 22:35:13 -05:00
Peter Maydell f1b237236c
exec.c: Don't set cpu->as until cpu_address_space_init
Rather than setting cpu->as unconditionally in cpu_exec_init
(and then having target-i386 override this later), don't set
it until the first call to cpu_address_space_init.

This requires us to initialise the address space for
both TCG and KVM (KVM doesn't need the AS listener but
it does require cpu->as to be set).

For target CPUs which don't set up any address spaces (currently
everything except i386), add the default address_space_memory
in qemu_init_vcpu().

Backports commit 56943e8cc14b7eeeab67d1942fa5d8bcafe3e53f from qemu
2018-02-17 22:24:36 -05:00
Richard Henderson a276496ebc
tcg: Adjust CODE_GEN_AVG_BLOCK_SIZE
At present, the "average" guestimate of TB size is way too small, leading
to many unused entries in the pre-allocated TB array. For a guest with 1GB
ram, we're currently allocating 256MB for the array.

Survey arm, alpha, aarch64, ppc, sparc, i686, x86_64 guests running on
x86_64 and ppc64 hosts and select a new average. The size of the array
drops to 81MB with no more flushing than before.

Backports commit 126d89e8cdfa3be15d51f76906eaccbcd0023f98 from qemu
2018-02-17 15:24:01 -05:00