x86_cpu_handle_mmu_fault is currently checking twice for writability
and executability of pages; the first time to decide whether to
trigger a page fault, the second time to compute the "prot" argument
to tlb_set_page_with_attrs.
Reorganize code so that first "prot" is computed, then it is used
to check whether to raise a page fault, then finally PROT_WRITE is
removed if the D bit will have to be set.
Backports commit 76c64d33601a4948d6f72022992574a75b6fab97 from qemu
These include page table walks, SVM accesses and SMM state save accesses.
The bulk of the patch is obtained with
sed -i 's/\(\<[a-z_]*_phys\(_notdirty\)\?\>(cs\)->as,/x86_\1,/'
Backports commit b216aa6c0fcbaa8ff4128969c14594896a5485a4 from qemu
