Re: [PATCH 40/60] kvm: x86: Handle IOAPIC EOIs per plane

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Critical] Iterating over all planes to call `vcpu_scan_ioapic(v)` corrupts the currently loaded hardware state (VMCS/VMCB) with inactive vCPU data.
- [High] `KVM_REQ_LOAD_EOI_EXITMAP` remains a common request, causing inactive planes to miss VMCS EOI exit map updates.
--

commit 2a25d5d833d92ddca988e436caa4350576bfb94b
Author: Joerg Roedel <joerg.roedel@amd.com>

Make sure the handling of IOAPIC EOIs is aware of planes.

This commit updates the IOAPIC EOI handling to filter routes by plane level.
It also modifies the KVM_REQ_SCAN_IOAPIC handling in vcpu_enter_guest() to
scan the IOAPIC for all vCPUs across planes instead of just the active one.

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 623838885753..a158740a6fc1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11336,8 +11336,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  				goto out;
>  			}
>  		}
> -		if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
> -			vcpu_scan_ioapic(vcpu);
> +		if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu)) {
> +			struct kvm_vcpu *v;
> +			unsigned i;
> +
> +			vcpu_for_each_plane(vcpu->common, i, v) {
> +				vcpu_scan_ioapic(v);
> +			}

[Severity: Critical]
Can iterating over all inactive planes here cause a regression in hardware
state?

When vcpu_scan_ioapic() is called for the inactive plane, it invokes
kvm_x86_call(sync_pir_to_irr)(v). In VMX, this architecture-specific sync
function executes vmread and vmwrite operations.

These instructions implicitly operate on the VMCS currently loaded on the
local physical CPU. Because the vCPU "v" is an inactive plane and does not
have its own VMCS loaded, could this result in the inactive plane's
interrupt data overwriting the currently active plane's VMCS, leading to
missed interrupts?

> +		}
>  		if (kvm_check_request(KVM_REQ_LOAD_EOI_EXITMAP, vcpu))
>  			vcpu_load_eoi_exitmap(vcpu);

[Severity: High]
Since KVM_REQ_LOAD_EOI_EXITMAP is not defined as a plane request, will
inactive planes miss VMCS EOI exit map updates?

Because KVM_REQ_LOAD_EOI_EXITMAP remains defined as KVM_ARCH_REQ(), it
is shared across the entire core/plane group. The first active plane to run
kvm_check_request() will clear this shared bit globally but only execute
vcpu_load_eoi_exitmap(vcpu) for itself.

When inactive planes subsequently run vcpu_enter_guest(), they will see the
shared request bit already cleared and skip their own updates, potentially
causing a regression in EOI intercept behavior.

Should KVM_REQ_LOAD_EOI_EXITMAP be converted to KVM_ARCH_PLANE_REQ?

>  		if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260608144252.351443-1-joro@8bytes.org?part=40