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target-i386: do not duplicate page protection checks 

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.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-11-17 17:09:33 +01:00
parent 3daa41078a
commit 76c64d3360
1 changed files with 24 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

67
target-i386/helper.c
View File

@ -890,38 +890,30 @@ do_check_protect_pse36:
goto do_fault_rsvd;
}
ptep ^= PG_NX_MASK;
if ((ptep & PG_NX_MASK) && is_write1 == 2) {
/* can the page can be put in the TLB? prot will tell us */
if (is_user && !(ptep & PG_USER_MASK)) {
goto do_fault_protect;
}
switch (mmu_idx) {
case MMU_USER_IDX:
if (!(ptep & PG_USER_MASK)) {
goto do_fault_protect;
}
if (is_write && !(ptep & PG_RW_MASK)) {
goto do_fault_protect;
}
break;
case MMU_KSMAP_IDX:
if (is_write1 != 2 && (ptep & PG_USER_MASK)) {
goto do_fault_protect;
prot = 0;
if (mmu_idx != MMU_KSMAP_IDX || !(ptep & PG_USER_MASK)) {
prot |= PAGE_READ;
if ((ptep & PG_RW_MASK) || (!is_user && !(env->cr[0] & CR0_WP_MASK))) {
prot |= PAGE_WRITE;
}
/* fall through */
case MMU_KNOSMAP_IDX:
if (is_write1 == 2 && (env->cr[4] & CR4_SMEP_MASK) &&
(ptep & PG_USER_MASK)) {
goto do_fault_protect;
}
if ((env->cr[0] & CR0_WP_MASK) &&
is_write && !(ptep & PG_RW_MASK)) {
goto do_fault_protect;
}
break;
default: /* cannot happen */
break;
}
if (!(ptep & PG_NX_MASK) &&
(mmu_idx == MMU_USER_IDX ||
!((env->cr[4] & CR4_SMEP_MASK) && (ptep & PG_USER_MASK)))) {
prot |= PAGE_EXEC;
}
if ((prot & (1 << is_write1)) == 0) {
goto do_fault_protect;
}
/* yes, it can! */
is_dirty = is_write && !(pte & PG_DIRTY_MASK);
if (!(pte & PG_ACCESSED_MASK) || is_dirty) {
pte |= PG_ACCESSED_MASK;
@ -931,25 +923,13 @@ do_check_protect_pse36:
x86_stl_phys_notdirty(cs, pte_addr, pte);
}
/* the page can be put in the TLB */
prot = PAGE_READ;
if (!(ptep & PG_NX_MASK) &&
(mmu_idx == MMU_USER_IDX ||
!((env->cr[4] & CR4_SMEP_MASK) && (ptep & PG_USER_MASK)))) {
prot |= PAGE_EXEC;
}
if (pte & PG_DIRTY_MASK) {
if (!(pte & PG_DIRTY_MASK)) {
/* only set write access if already dirty... otherwise wait
for dirty access */
if (is_user) {
if (ptep & PG_RW_MASK)
prot |= PAGE_WRITE;
} else {
if (!(env->cr[0] & CR0_WP_MASK) ||
(ptep & PG_RW_MASK))
prot |= PAGE_WRITE;
}
assert(!is_write);
prot &= ~PAGE_WRITE;
}
do_mapping:
pte = pte & env->a20_mask;
@ -962,6 +942,7 @@ do_check_protect_pse36:
page_offset = vaddr & (page_size - 1);
paddr = pte + page_offset;
assert(prot & (1 << is_write1));
tlb_set_page_with_attrs(cs, vaddr, paddr, cpu_get_mem_attrs(env),
prot, mmu_idx, page_size);
return 0;