[PATCH] KVM: X86: Sanity check on gfn before removal

[PATCH] KVM: X86: Sanity check on gfn before removal

[Peter Xu]

The index returned by kvm_async_pf_gfn_slot() will be removed when an
async pf gfn is going to be removed.  However kvm_async_pf_gfn_slot()
is not reliable in that it can return the last key it loops over even
if the gfn is not found in the async gfn array.  It should never
happen, but it's still better to sanity check against that to make
sure no unexpected gfn will be removed.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 arch/x86/kvm/x86.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fc74dafa72ff..f1c6e604dd12 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10308,6 +10308,10 @@ static void kvm_del_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
 	u32 i, j, k;
 
 	i = j = kvm_async_pf_gfn_slot(vcpu, gfn);
+
+	if (WARN_ON_ONCE(vcpu->arch.apf.gfns[i] != gfn))
+		return;
+
 	while (true) {
 		vcpu->arch.apf.gfns[i] = ~0;
 		do {
-- 
2.24.1

Re: [PATCH] KVM: X86: Sanity check on gfn before removal

[Paolo Bonzini]

On 16/04/20 17:59, Peter Xu wrote:
> The index returned by kvm_async_pf_gfn_slot() will be removed when an
> async pf gfn is going to be removed.  However kvm_async_pf_gfn_slot()
> is not reliable in that it can return the last key it loops over even
> if the gfn is not found in the async gfn array.  It should never
> happen, but it's still better to sanity check against that to make
> sure no unexpected gfn will be removed.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  arch/x86/kvm/x86.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fc74dafa72ff..f1c6e604dd12 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10308,6 +10308,10 @@ static void kvm_del_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
>  	u32 i, j, k;
>  
>  	i = j = kvm_async_pf_gfn_slot(vcpu, gfn);
> +
> +	if (WARN_ON_ONCE(vcpu->arch.apf.gfns[i] != gfn))
> +		return;
> +
>  	while (true) {
>  		vcpu->arch.apf.gfns[i] = ~0;
>  		do {
> 

Queued, thanks.

Paolo