linux-kernel - Re: [Part2 PATCH v5 15/31] KVM: SVM: Reserve ASID range for SEV guest

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Date:   Fri, 13 Oct 2017 18:58:21 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [Part2 PATCH v5 15/31] KVM: SVM: Reserve ASID range for SEV guest

On Wed, Oct 04, 2017 at 08:13:56AM -0500, Brijesh Singh wrote:
> A SEV-enabled guest must use ASIDs from the defined subset, while non-SEV
> guests can use the remaining ASID range. The range of allowed SEV guest
> ASIDs is [1 - CPUID_8000_001F[ECX][31:0]].
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/kvm/svm.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index be2e98c01b22..3244b8f88010 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -323,6 +323,8 @@ enum {
>  
>  #define VMCB_AVIC_APIC_BAR_MASK		0xFFFFFFFFFF000ULL
>  
> +static unsigned int max_sev_asid;
> +
>  static inline void mark_all_dirty(struct vmcb *vmcb)
>  {
>  	vmcb->control.clean = 0;
> @@ -787,7 +789,7 @@ static int svm_hardware_enable(void)
>  	sd->asid_generation = 1;
>  	sd->max_asid = cpuid_ebx(SVM_CPUID_FUNC) - 1;
>  	sd->next_asid = sd->max_asid + 1;
> -	sd->min_asid = 1;
> +	sd->min_asid = max_sev_asid + 1;
>  
>  	gdt = get_current_gdt_rw();
>  	sd->tss_desc = (struct kvm_ldttss_desc *)(gdt + GDT_ENTRY_TSS);
> @@ -1054,6 +1056,15 @@ static int avic_ga_log_notifier(u32 ga_tag)
>  	return 0;
>  }
>  
> +/*
> + * Get maximum number of encrypted guest supported: Fn8001_001F[ECX].
> + *     [31:0]: Number of supported guest
> + */
> +static __init void sev_hardware_setup(void)
> +{
> +	max_sev_asid = cpuid_ecx(0x8000001F);
> +}
> +
>  static __init int svm_hardware_setup(void)
>  {
>  	int cpu;
> @@ -1084,6 +1095,16 @@ static __init int svm_hardware_setup(void)
>  		kvm_tsc_scaling_ratio_frac_bits = 32;
>  	}
>  
> +	if (sev) {
> +		if (!boot_cpu_has(X86_FEATURE_SEV) ||
> +		    !IS_ENABLED(CONFIG_KVM_AMD_SEV)) {
> +			sev = false;
> +		} else {
> +			sev_hardware_setup();
> +			pr_info("SEV supported\n");
> +		}
> +	}

Flip that logic:

---
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3244b8f88010..d4b62536e305 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1057,8 +1057,8 @@ static int avic_ga_log_notifier(u32 ga_tag)
 }
 
 /*
- * Get maximum number of encrypted guest supported: Fn8001_001F[ECX].
- *     [31:0]: Number of supported guest
+ * Get the maximum number of encrypted guests:
+ *  Fn8001_001F[ECX][31:0]: Number of supported guests.
  */
 static __init void sev_hardware_setup(void)
 {
@@ -1096,12 +1096,12 @@ static __init int svm_hardware_setup(void)
 	}
 
 	if (sev) {
-		if (!boot_cpu_has(X86_FEATURE_SEV) ||
-		    !IS_ENABLED(CONFIG_KVM_AMD_SEV)) {
-			sev = false;
-		} else {
+		if (boot_cpu_has(X86_FEATURE_SEV) &&
+		    IS_ENABLED(CONFIG_KVM_AMD_SEV)) {
 			sev_hardware_setup();
 			pr_info("SEV supported\n");
+		} else {
+			sev = false;
 		}
 	}
 
-- 
Regards/Gruss,
    Boris.

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