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Message-ID: <ZVGzC66k0QtJywi0@chao-email>
Date: Mon, 13 Nov 2023 13:24:27 +0800
From: Chao Gao <chao.gao@...el.com>
To: Xin Li <xin3.li@...el.com>
CC: <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <linux-hyperv@...r.kernel.org>,
<linux-kselftest@...r.kernel.org>, <seanjc@...gle.com>,
<pbonzini@...hat.com>, <corbet@....net>, <kys@...rosoft.com>,
<haiyangz@...rosoft.com>, <wei.liu@...nel.org>,
<decui@...rosoft.com>, <tglx@...utronix.de>, <mingo@...hat.com>,
<bp@...en8.de>, <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
<hpa@...or.com>, <vkuznets@...hat.com>, <peterz@...radead.org>,
<ravi.v.shankar@...el.com>
Subject: Re: [PATCH v1 10/23] KVM: VMX: Add support for FRED context
save/restore
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 2c924075f6f1..c5a55810647f 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -1451,6 +1451,9 @@ static const u32 msrs_to_save_base[] = {
> MSR_STAR,
> #ifdef CONFIG_X86_64
> MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
>+ MSR_IA32_FRED_RSP0, MSR_IA32_FRED_RSP1, MSR_IA32_FRED_RSP2,
>+ MSR_IA32_FRED_RSP3, MSR_IA32_FRED_STKLVLS, MSR_IA32_FRED_SSP1,
>+ MSR_IA32_FRED_SSP2, MSR_IA32_FRED_SSP3, MSR_IA32_FRED_CONFIG,
Need to handle the case where FRED MSRs are valid but KVM cannot virtualize
FRED, see kvm_probe_msr_to_save().
> #endif
> MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
> MSR_IA32_FEAT_CTL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
>@@ -1890,6 +1893,16 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
>
> data = (u32)data;
> break;
>+ case MSR_IA32_FRED_RSP0 ... MSR_IA32_FRED_CONFIG:
>+ if (host_initiated || guest_cpuid_has(vcpu, X86_FEATURE_FRED))
>+ break;
Nothing guarantees FRED MSRs/VMCS fields exist on the hardware here. Probably use
guest_cpu_cap_has()*.
*: https://lore.kernel.org/kvm/20231110235528.1561679-1-seanjc@google.com
>+
>+ /*
>+ * Inject #GP upon FRED MSRs accesses from a non-FRED guest to
>+ * make sure no malicious guest can write to FRED MSRs thus to
>+ * corrupt host FRED MSRs.
>+ */
I think injecting #GP here is simply because KVM should emulate hardware
behavior. To me, preventing guest from corrupting FRED MSRs is at most a
byproduct. I prefer to drop the comment.
>+ return 1;
> }
>
> msr.data = data;
>@@ -1933,6 +1946,16 @@ int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
> !guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
> return 1;
> break;
>+ case MSR_IA32_FRED_RSP0 ... MSR_IA32_FRED_CONFIG:
>+ if (host_initiated || guest_cpuid_has(vcpu, X86_FEATURE_FRED))
>+ break;
>+
>+ /*
>+ * Inject #GP upon FRED MSRs accesses from a non-FRED guest to
>+ * make sure no malicious guest can write to FRED MSRs thus to
>+ * corrupt host FRED MSRs.
>+ */
>+ return 1;
> }
>
> msr.index = index;
>--
>2.42.0
>
>
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