Re: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused cmpxchg to be not atomic

Vitaly Kuznetsov
2022-05-12T12:46:12Z

Maxim Levitsky <mlevitsk@redhat.com> writes:

> Fixes: 1c2361f667f36 ("KVM: x86: Use __try_cmpxchg_user() to emulate atomic accesses")
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
> arch/x86/kvm/x86.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Yes, this is the root cause of the TDP mmu leak I was doing debug of in the last week.
> Non working cmpxchg on which TDP mmu relies makes it install two differnt shadow pages
> under same spte.

In case the fix is not squashed with 1c2361f667f36, the above should
really go before '---'.

>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8ee8c91fa7625..79cabd3d97d22 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7329,7 +7329,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
> goto emul_write;
>
> hva = kvm_vcpu_gfn_to_hva(vcpu, gpa_to_gfn(gpa));
> - if (kvm_is_error_hva(addr))
> + if (kvm_is_error_hva(hva))

Looks like a typo indeed, so

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

> goto emul_write;
>
> hva += offset_in_page(gpa);

--
Vitaly