From b19ee2ff3b287fea48a2896a381e31319394fe58 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Wed, 11 May 2016 08:04:29 -0700 Subject: [PATCH] KVM: x86: avoid write-tearing of TDP MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Radim Krčmář --- arch/x86/kvm/mmu.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 24e8001..def97b3 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -336,12 +336,12 @@ static gfn_t pse36_gfn_delta(u32 gpte) #ifdef CONFIG_X86_64 static void __set_spte(u64 *sptep, u64 spte) { - *sptep = spte; + WRITE_ONCE(*sptep, 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) @@ -390,7 +390,7 @@ static void __set_spte(u64 *sptep, u64 spte) */ 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) @@ -400,7 +400,7 @@ static void __update_clear_spte_fast(u64 *sptep, u64 spte) ssptep = (union split_spte *)sptep; 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 -- 2.7.4