2022-04-27 16:25:45

by Sasha Levin

Subject: [PATCH MANUALSEL 5.17 4/7] KVM: x86: Do not change ICR on write to APIC_SELF_IPI

From: Paolo Bonzini <[email protected]>

[ Upstream commit d22a81b304a27fca6124174a8e842e826c193466 ]

Emulating writes to SELF_IPI with a write to ICR has an unwanted side effect:
the value of ICR in vAPIC page gets changed. The lists SELF_IPI as write-only,
with no associated MMIO offset, so any write should have no visible side
effect in the vAPIC page.

Reported-by: Chao Gao <[email protected]>
Reviewed-by: Sean Christopherson <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
arch/x86/kvm/lapic.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 2a10d0033c96..6b6f9359d29e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2125,10 +2125,9 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
break;

case APIC_SELF_IPI:
- if (apic_x2apic_mode(apic)) {
- kvm_lapic_reg_write(apic, APIC_ICR,
- APIC_DEST_SELF | (val & APIC_VECTOR_MASK));
- } else
+ if (apic_x2apic_mode(apic))
+ kvm_apic_send_ipi(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK), 0);
+ else
ret = 1;
break;
default:
--
2.35.1

2022-04-27 16:50:01

by Paolo Bonzini

Subject: Re: [PATCH MANUALSEL 5.17 4/7] KVM: x86: Do not change ICR on write to APIC_SELF_IPI

On 4/27/22 17:54, Sasha Levin wrote:
> From: Paolo Bonzini <[email protected]>
>
> [ Upstream commit d22a81b304a27fca6124174a8e842e826c193466 ]
>
> Emulating writes to SELF_IPI with a write to ICR has an unwanted side effect:
> the value of ICR in vAPIC page gets changed. The lists SELF_IPI as write-only,
> with no associated MMIO offset, so any write should have no visible side
> effect in the vAPIC page.
>
> Reported-by: Chao Gao <[email protected]>
> Reviewed-by: Sean Christopherson <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>
> Signed-off-by: Sasha Levin <[email protected]>
> ---
> arch/x86/kvm/lapic.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 2a10d0033c96..6b6f9359d29e 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2125,10 +2125,9 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
> break;
>
> case APIC_SELF_IPI:
> - if (apic_x2apic_mode(apic)) {
> - kvm_lapic_reg_write(apic, APIC_ICR,
> - APIC_DEST_SELF | (val & APIC_VECTOR_MASK));
> - } else
> + if (apic_x2apic_mode(apic))
> + kvm_apic_send_ipi(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK), 0);
> + else
> ret = 1;
> break;
> default:

Acked-by: Paolo Bonzini <[email protected]>