Re: [PATCH -v5.1] x86/kvm: Implement HWCR support

[Sean Christopherson]

On Thu, Apr 18, 2019 at 02:28:50PM +0200, Borislav Petkov wrote:
> Hi all,
> 
> ok here's v5.1 with most of Sean's feedback addressed. The function
> checking whether HWCR[18] is set, I've renamed to can_set_mci_status()
> and left it to return bool because it really is used in boolean context,
> answering the question "Can I set MCi_STATUS MSRs?"
> 
> And now it all looks simple and clean, just how I like it! :-)
> 
> Thx.
> 
> ---
> From: Borislav Petkov <bp@xxxxxxx>
> 
> The hardware configuration register has some useful bits which can be
> used by guests. Implement McStatusWrEn which can be used by guests when
> injecting MCEs with the in-kernel mce-inject module.
> 
> For that, we need to set bit 18 - McStatusWrEn - first, before writing
> the MCi_STATUS registers (otherwise we #GP).
> 
> Add the required machinery to do so.
> 
> Signed-off-by: Borislav Petkov <bp@xxxxxxx>
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: Joerg Roedel <joro@xxxxxxxxxx>
> Cc: KVM <kvm@xxxxxxxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Yazen Ghannam <Yazen.Ghannam@xxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |  3 +++
>  arch/x86/kvm/x86.c              | 33 +++++++++++++++++++++++++++------
>  2 files changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 159b5988292f..541c431df806 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -780,6 +780,9 @@ struct kvm_vcpu_arch {
>  
>  	/* Flush the L1 Data cache for L1TF mitigation on VMENTER */
>  	bool l1tf_flush_l1d;
> +
> +	/* AMD MSRC001_0015 Hardware Configuration */
> +	u64 msr_hwcr;
>  };
>  
>  struct kvm_lpage_info {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 099b851dabaf..10f6acc6494c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2273,6 +2273,18 @@ static void kvmclock_sync_fn(struct work_struct *work)
>  					KVMCLOCK_SYNC_PERIOD);
>  }
>  
> +/*
> + * On AMD, HWCR[McStatusWrEn] controls whether setting MCi_STATUS results in #GP.
> + */
> +static bool can_set_mci_status(struct kvm_vcpu *vcpu)
> +{
> +	/* McStatusWrEn enabled? */
> +	if (guest_cpuid_is_amd(vcpu))
> +		return !!(vcpu->arch.msr_hwcr & BIT_ULL(18));
> +
> +	return false;
> +}
> +
>  static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  {
>  	u64 mcg_cap = vcpu->arch.mcg_cap;
> @@ -2304,9 +2316,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  			if ((offset & 0x3) == 0 &&
>  			    data != 0 && (data | (1 << 10)) != ~(u64)0)
>  				return -1;
> -			if (!msr_info->host_initiated &&
> -				(offset & 0x3) == 1 && data != 0)
> -				return -1;
> +
> +			/* MCi_STATUS */
> +			if ((offset & 0x3) == 1 && !msr_info->host_initiated) {
> +				if (!can_set_mci_status(vcpu))

This doesn't allow writing '0' regardless of msr_hwcr.BIT(18), which was
previously supported.  And there's no need for multiple if statements.

> +					return -1;
> +			}
> +
>  			vcpu->arch.mce_banks[offset] = data;
>  			break;
>  		}
> @@ -2455,8 +2471,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		data &= ~(u64)0x40;	/* ignore flush filter disable */
>  		data &= ~(u64)0x100;	/* ignore ignne emulation enable */
>  		data &= ~(u64)0x8;	/* ignore TLB cache disable */
> -		data &= ~(u64)0x40000;  /* ignore Mc status write enable */
> -		if (data != 0) {
> +
> +		/* Handle McStatusWrEn */
> +		if (data == BIT_ULL(18)) {
> +			vcpu->arch.msr_hwcr = data;
> +		} else if (data != 0) {
>  			vcpu_unimpl(vcpu, "unimplemented HWCR wrmsr: 0x%llx\n",
>  				    data);
>  			return 1;
> @@ -2730,7 +2749,6 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_K8_SYSCFG:
>  	case MSR_K8_TSEG_ADDR:
>  	case MSR_K8_TSEG_MASK:
> -	case MSR_K7_HWCR:
>  	case MSR_VM_HSAVE_PA:
>  	case MSR_K8_INT_PENDING_MSG:
>  	case MSR_AMD64_NB_CFG:
> @@ -2894,6 +2912,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_MISC_FEATURES_ENABLES:
>  		msr_info->data = vcpu->arch.msr_misc_features_enables;
>  		break;
> +	case MSR_K7_HWCR:
> +		msr_info->data = vcpu->arch.msr_hwcr;
> +		break;
>  	default:
>  		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
>  			return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
> -- 
> 2.21.0
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> Good mailing practices for 400: avoid top-posting and trim the reply.