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KVM: x86: avoid write-tearing of TDP 

In theory, nothing prevents the compiler from write-tearing PTEs, or
split PTE writes. These partially-modified PTEs can be fetched by other
cores and cause mayhem. I have not really encountered such case in
real-life, but it does seem possible.

For example, the compiler may try to do something creative for
kvm_set_pte_rmapp() and perform multiple writes to the PTE.

Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
This commit is contained in:
Nadav Amit 2016-05-11 08:04:29 -07:00 committed by Radim Krčmář
parent 13e98fd1ef
commit b19ee2ff3b
1 changed files with 4 additions and 4 deletions
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8
arch/x86/kvm/mmu.c
View File

@ -336,12 +336,12 @@ static gfn_t pse36_gfn_delta(u32 gpte)
#ifdef CONFIG_X86_64 #ifdef CONFIG_X86_64
static void __set_spte(u64 *sptep, u64 spte) static void __set_spte(u64 *sptep, u64 spte)
{ {
*sptep = spte; WRITE_ONCE(*sptep, spte);
} }
static void __update_clear_spte_fast(u64 *sptep, u64 spte) static void __update_clear_spte_fast(u64 *sptep, u64 spte)
{ {
*sptep = spte; WRITE_ONCE(*sptep, spte);
} }
static u64 __update_clear_spte_slow(u64 *sptep, u64 spte) static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
@ -390,7 +390,7 @@ static void __set_spte(u64 *sptep, u64 spte)
*/ */
smp_wmb(); smp_wmb();
ssptep->spte_low = sspte.spte_low; WRITE_ONCE(ssptep->spte_low, sspte.spte_low);
} }
static void __update_clear_spte_fast(u64 *sptep, u64 spte) static void __update_clear_spte_fast(u64 *sptep, u64 spte)
@ -400,7 +400,7 @@ static void __update_clear_spte_fast(u64 *sptep, u64 spte)
ssptep = (union split_spte *)sptep; ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte; sspte = (union split_spte)spte;
ssptep->spte_low = sspte.spte_low; WRITE_ONCE(ssptep->spte_low, sspte.spte_low);
/* /*
* If we map the spte from present to nonpresent, we should clear * If we map the spte from present to nonpresent, we should clear