I mistakenly sent this patch with wrong date, which is hopefully the
reason you ignored it.
So this email is in order to bump it up.
Thanks,
Nadav
Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
> 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@xxxxxxxxx>
> ---
> 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 1ff4dbb..4fca1cb 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
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