KVM: x86: avoid write-tearing of TDP (b19ee2ff) · Commits · 戴 / test

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>

arch/x86/kvm/mmu.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -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

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