>From 64ff7eb90d0e3b044fb423c6d073b3966f866eb3 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 13 Jun 2024 10:10:11 -0700 Subject: [PATCH 04/28] KVM: VMX: Don't modify guest XFD_ERR if CR0.TS=1 Don't update the guest's XFD_ERR MSR if CR0.TS is set; per the SDM, XFD_ERR is not modified if CR0.TS=1. Although it's not explicitly stated in the SDM, conceptually it makes sense the CR0.TS check would be done prior to the XFD_ERR check, e.g. CR0.TS=1 blocks all SIMD state, whereas XFD blocks only XTILE state. Device-not-available exceptions that are not due to XFD - those resulting from setting CR0.TS to 1 - do not modify the IA32_XFD_ERR MSR. Opportunistically update the comment to call out that XFD_ERR is updated before the VM-Exit check occurs. Nothing in the SDM explicitly calls out this behavior, but logically it must be the behavior, otherwise reading XFD_ERR in handle_nm_fault_irqoff() would return stale data, i.e. the to-be-delivered XFD_ERR value would need to be saved in EXIT_QUALIFICATION, a la DR6 for #DB and CR2 for #PF, so that software could capture the guest value. Fixes: ec5be88ab29f ("kvm: x86: Intercept #NM for saving IA32_XFD_ERR") Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/vmx.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 8485fd1e28eb..16c91a78fc2b 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6923,16 +6923,16 @@ static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu) * MSR value is not clobbered by the host activity before the guest * has chance to consume it. * - * Do not blindly read xfd_err here, since this exception might - * be caused by L1 interception on a platform which doesn't - * support xfd at all. + * Update the guest's XFD_ERR if and only if XFD is enabled, as the #NM + * interception may have been caused by L1 interception. Per the SDM, + * XFD_ERR is not modified if CR0.TS=1. * - * Do it conditionally upon guest_fpu::xfd. xfd_err matters - * only when xfd contains a non-zero value. - * - * Queuing exception is done in vmx_handle_exit. See comment there. + * Note, XFD_ERR is updated _before_ the #NM interception check, i.e. + * unlike CR2 and DR6, the value is not a payload that is attached to + * the #NM exception. */ - if (vcpu->arch.guest_fpu.fpstate->xfd) + if (vcpu->arch.guest_fpu.fpstate->xfd && + !kvm_is_cr0_bit_set(vcpu, X86_CR0_TS)) rdmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err); } -- 2.45.2.627.g7a2c4fd464-goog