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Commit b19ee2ff authored by Nadav Amit's avatar Nadav Amit Committed by Radim Krčmář
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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: default avatarNadav Amit <nadav.amit@gmail.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent 13e98fd1

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