Hi Zenghui, Marc,
On 10/29/19 8:19 AM, Zenghui Yu wrote:
> It's possible that two LPIs locate in the same "byte_offset" but target
> two different vcpus, where their pending status are indicated by two
> different pending tables. In such a scenario, using last_byte_offset
> optimization will lead KVM relying on the wrong pending table entry.
> Let us use last_ptr instead, which can be treated as a byte index into
> a pending table and also, can be vcpu specific.
>
> Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> ---
>
> If this patch has done the right thing, we can even add the:
>
> Fixes: 280771252c1b ("KVM: arm64: vgic-v3: KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES")
>
> But to be honest, I'm not clear about what has this patch actually fixed.
> Pending tables should contain all zeros before we flush vgic_irq's pending
> status into guest's RAM (thinking that guest should never write anything
> into it). So the pending table entry we've read from the guest memory
> seems always be zero. And we will always do the right thing even if we
> rely on the wrong pending table entry.
>
> I think I must have some misunderstanding here... Please fix me.
>
> virt/kvm/arm/vgic/vgic-v3.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index 5ef93e5041e1..7cd2e2f81513 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -363,8 +363,8 @@ int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq)
> int vgic_v3_save_pending_tables(struct kvm *kvm)
> {
> struct vgic_dist *dist = &kvm->arch.vgic;
> - int last_byte_offset = -1;
> struct vgic_irq *irq;
> + gpa_t last_ptr = -1;
> int ret;
> u8 val;
>
> @@ -384,11 +384,11 @@ int vgic_v3_save_pending_tables(struct kvm *kvm)
> bit_nr = irq->intid % BITS_PER_BYTE;
> ptr = pendbase + byte_offset;
>
> - if (byte_offset != last_byte_offset) {
> + if (ptr != last_ptr) {
> ret = kvm_read_guest_lock(kvm, ptr, &val, 1);
> if (ret)
> return ret;
> - last_byte_offset = byte_offset;
> + last_ptr = ptr;
> }
>
> stored = val & (1U << bit_nr);
>
Acked-by: Eric Auger <eric.auger@xxxxxxxxxx>
Thanks for fixing this.
Eric
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