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target-arm: Handle "extended small page" descriptors correctly

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The old ARMv5-style page table format includes a kind of second level
descriptor named the "extended small page" format, whose primary purpose
is to allow specification of the TEX memory attribute bits on a 4K page.
This exists on ARMv6 and also (as an implementation extension) on XScale
CPUs; it's UNPREDICTABLE on v5.

We were mishandling this in two ways:
(1) we weren't implementing it for v6 (probably never noticed because
Linux will use the new-style v6 page table format there)
(2) we were not correctly setting the page_size, which is 4K, not 1K

The latter bug went unnoticed for years because the only thing which
the page_size affects is which TLB entries get flushed when the guest
does a TLB invalidate on an address in the page, and prior to commit
2f0d8631b7 we were doing a full TLB flush very frequently due to Linux's
habit of writing the SCTLR pointlessly a lot.

(We can assume that after commit 2f0d8631b7 the bug went unnoticed
for a year because nobody's actually using the Zaurus/XScale emulation...)

Report the correct page size for these descriptors, and permit them
on ARMv6 CPUs. This fixes a problem where a kernel image for Zaurus
can boot the kernel OK but gets random segfaults when it tries to
run userspace programs.

Backports commit fc1891c74ae122a9dc7854f38bae7db03cd911e6 from qemu
This commit is contained in:
Peter Maydell 2018-02-13 14:17:17 -05:00 committed by Lioncash
parent 3d72ec65bd
commit 84c75286f5
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 9 additions and 4 deletions
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13
qemu/target-arm/helper.c
View file

@ -4763,20 +4763,25 @@ static int get_phys_addr_v5(CPUARMState *env, uint32_t address, int access_type,
ap = (desc >> (4 + ((address >> 9) & 6))) & 3;
*page_size = 0x1000;
break;
case 3: /* 1k page. */
case 3: /* 1k page, or ARMv6/XScale "extended small (4k) page" */
if (type == 1) {
if (arm_feature(env, ARM_FEATURE_XSCALE)) {
/* ARMv6/XScale extended small page format */
if (arm_feature(env, ARM_FEATURE_XSCALE)
|| arm_feature(env, ARM_FEATURE_V6)) {
phys_addr = (desc & 0xfffff000) | (address & 0xfff);
*page_size = 0x1000;
} else {
/* Page translation fault. */
/* UNPREDICTABLE in ARMv5; we choose to take a
* page translation fault.
*/
code = 7;
goto do_fault;
}
} else {
phys_addr = (desc & 0xfffffc00) | (address & 0x3ff);
*page_size = 0x400;
}
ap = (desc >> 4) & 3;
*page_size = 0x400;
break;
default:
/* Never happens, but compiler isn't smart enough to tell. */