linux-kernel - RE: [PATCH v1 09/23] KVM: VMX: Switch FRED RSP0 between host and guest

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Message-ID: <SA1PR11MB67345297BC929DB49B422D2FA8B2A@SA1PR11MB6734.namprd11.prod.outlook.com>
Date:   Tue, 14 Nov 2023 05:17:45 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     "Gao, Chao" <chao.gao@...el.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
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        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v1 09/23] KVM: VMX: Switch FRED RSP0 between host and
 guest

> >+	if (cpu_feature_enabled(X86_FEATURE_FRED) &&
> >+	    guest_cpuid_has(&vmx->vcpu, X86_FEATURE_FRED)) {
> 
> IIUC, vmx_prepare_switch_to_host() is called from IRQ-disabled context. using
> guest_cpuid_has() in this context is not desired, see
> lockdep_assert_irqs_enabled() in cpuid_entry2_find().

Nice catch!

Anyway it's a bad idea to do a search call here, let me find a better way
for all FRED CPUID checks.

> >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index
> >f8c02bd37069..328a3447f064 100644
> >--- a/arch/x86/kvm/vmx/vmx.h
> >+++ b/arch/x86/kvm/vmx/vmx.h
> >@@ -276,6 +276,8 @@ struct vcpu_vmx {
> > #ifdef CONFIG_X86_64
> > 	u64		      msr_host_kernel_gs_base;
> > 	u64		      msr_guest_kernel_gs_base;
> >+	u64		      msr_host_fred_rsp0;
> >+	u64		      msr_guest_fred_rsp0;
> 
> resetting guest fred rsp0 to 0 during vcpu reset is missing.

hmm, I assume it gets the same treatment as guest_kernel_gs_base.

It seems we don't reset guest_kernel_gs_base.  No?