linux-kernel - Re: [PATCH 3/4] KVM: nVMX: accurate emulation of MSR_IA32_CR{0,4}

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Date:   Wed, 23 Nov 2016 04:06:17 -0500 (EST)
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        jmattson@...gle.com, rkrcmar@...hat.com
Subject: Re: [PATCH 3/4] KVM: nVMX: accurate emulation of
 MSR_IA32_CR{0,4}_FIXED1


> Set MSR_IA32_CR{0,4}_FIXED1 to match the CPU's MSRs.
> 
> In addition, MSR_IA32_CR4_FIXED1 should reflect the available CR4 bits
> according to CPUID. Whenever guest CPUID is updated by userspace,
> regenerate MSR_IA32_CR4_FIXED1 to match it.
> 
> Signed-off-by: David Matlack <dmatlack@...gle.com>

Oh, I thought userspace would do that!  Doing it in KVM is fine as well,
but then do we need to give userspace access to CR{0,4}_FIXED{0,1} at all?

Paolo

> ---
> Note: "x86/cpufeature: Add User-Mode Instruction Prevention definitions" has
> not hit kvm/master yet so the macros for X86_CR4_UMIP and X86_FEATURE_UMIP
> are not available.
> 
>  arch/x86/kvm/vmx.c | 54
>  +++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 51 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index a2a5ad8..ac5d9c0 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2852,16 +2852,18 @@ static void nested_vmx_setup_ctls_msrs(struct
> vcpu_vmx *vmx)
>  		vmx->nested.nested_vmx_basic |= VMX_BASIC_INOUT;
>  
>  	/*
> -	 * These MSRs specify bits which the guest must keep fixed (on or off)
> +	 * These MSRs specify bits which the guest must keep fixed on
>  	 * while L1 is in VMXON mode (in L1's root mode, or running an L2).
>  	 * We picked the standard core2 setting.
>  	 */
>  #define VMXON_CR0_ALWAYSON     (X86_CR0_PE | X86_CR0_PG | X86_CR0_NE)
>  #define VMXON_CR4_ALWAYSON     X86_CR4_VMXE
>  	vmx->nested.nested_vmx_cr0_fixed0 = VMXON_CR0_ALWAYSON;
> -	vmx->nested.nested_vmx_cr0_fixed1 = -1ULL;
>  	vmx->nested.nested_vmx_cr4_fixed0 = VMXON_CR4_ALWAYSON;
> -	vmx->nested.nested_vmx_cr4_fixed1 = -1ULL;
> +
> +	/* These MSRs specify bits which the guest must keep fixed off. */
> +	rdmsrl(MSR_IA32_VMX_CR0_FIXED1, vmx->nested.nested_vmx_cr0_fixed1);
> +	rdmsrl(MSR_IA32_VMX_CR4_FIXED1, vmx->nested.nested_vmx_cr4_fixed1);
>  
>  	/* highest index: VMX_PREEMPTION_TIMER_VALUE */
>  	vmx->nested.nested_vmx_vmcs_enum = 0x2e;
> @@ -9580,6 +9582,49 @@ static void vmcs_set_secondary_exec_control(u32
> new_ctl)
>  		     (new_ctl & ~mask) | (cur_ctl & mask));
>  }
>  
> +/*
> + * Generate MSR_IA32_VMX_CR4_FIXED1 according to CPUID. Only set bits
> + * (indicating "allowed-1") if they are supported in the guest's CPUID.
> + */
> +static void nested_vmx_cr4_fixed1_update(struct kvm_vcpu *vcpu)
> +{
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	struct kvm_cpuid_entry2 *entry;
> +
> +#define update(_cr4_mask, _reg, _cpuid_mask) do {			\
> +	if (entry && (entry->_reg & (_cpuid_mask)))			\
> +		vmx->nested.nested_vmx_cr4_fixed1 |= (_cr4_mask);	\
> +} while (0)
> +
> +	vmx->nested.nested_vmx_cr4_fixed1 = X86_CR4_PCE;
> +
> +	entry = kvm_find_cpuid_entry(vcpu, 0x1, 0);
> +	update(X86_CR4_VME,        edx, bit(X86_FEATURE_VME));
> +	update(X86_CR4_PVI,        edx, bit(X86_FEATURE_VME));
> +	update(X86_CR4_TSD,        edx, bit(X86_FEATURE_TSC));
> +	update(X86_CR4_DE,         edx, bit(X86_FEATURE_DE));
> +	update(X86_CR4_PSE,        edx, bit(X86_FEATURE_PSE));
> +	update(X86_CR4_PAE,        edx, bit(X86_FEATURE_PAE));
> +	update(X86_CR4_MCE,        edx, bit(X86_FEATURE_MCE));
> +	update(X86_CR4_PGE,        edx, bit(X86_FEATURE_PGE));
> +	update(X86_CR4_OSFXSR,     edx, bit(X86_FEATURE_FXSR));
> +	update(X86_CR4_OSXMMEXCPT, edx, bit(X86_FEATURE_XMM));
> +	update(X86_CR4_VMXE,       ecx, bit(X86_FEATURE_VMX));
> +	update(X86_CR4_SMXE,       ecx, bit(X86_FEATURE_SMX));
> +	update(X86_CR4_PCIDE,      ecx, bit(X86_FEATURE_PCID));
> +	update(X86_CR4_OSXSAVE,    ecx, bit(X86_FEATURE_XSAVE));
> +
> +	entry = kvm_find_cpuid_entry(vcpu, 0x7, 0);
> +	update(X86_CR4_FSGSBASE,   ebx, bit(X86_FEATURE_FSGSBASE));
> +	update(X86_CR4_SMEP,       ebx, bit(X86_FEATURE_SMEP));
> +	update(X86_CR4_SMAP,       ebx, bit(X86_FEATURE_SMAP));
> +	update(X86_CR4_PKE,        ecx, bit(X86_FEATURE_PKU));
> +	/* TODO: Use X86_CR4_UMIP and X86_FEATURE_UMIP macros */
> +	update(bit(11),            ecx, bit(2));
> +
> +#undef update
> +}
> +
>  static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpuid_entry2 *best;
> @@ -9621,6 +9666,9 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>  	else
>  		to_vmx(vcpu)->msr_ia32_feature_control_valid_bits &=
>  			~FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
> +
> +	if (nested_vmx_allowed(vcpu))
> +		nested_vmx_cr4_fixed1_update(vcpu);
>  }
>  
>  static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2
>  *entry)
> --
> 2.8.0.rc3.226.g39d4020
> 
>