linux-kernel - Re: [RFC Part2 PATCH v3 05/26] KVM: SVM: Reserve ASID range for SEV guest

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Message-ID: <20170912200416.ygcsqvznkkp2gd7r@pd.tnic>
Date:   Tue, 12 Sep 2017 22:04:16 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        \"Radim Krčmář\" <rkrcmar@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFC Part2 PATCH v3 05/26] KVM: SVM: Reserve ASID range for SEV
 guest

On Mon, Jul 24, 2017 at 03:02:42PM -0500, Brijesh Singh wrote:
> SEV-enabled guest must use ASIDs from the defined subset, while non-SEV

"A SEV-enabled ..."

> guests can use the remaining ASID range. The range of ASID allowed for
> SEV-enabled guest is from 1 to a maximum value defined via CPUID
> Fn8000_001f[ECX].

I'd rewrite that to:

"The range of allowed SEV guest ASIDs is [1 - CPUID_8000_001F[ECX][31:0]]".

> 
> 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 46f41bb..06bd902 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -319,6 +319,9 @@ enum {
>  
>  #define VMCB_AVIC_APIC_BAR_MASK		0xFFFFFFFFFF000ULL
>  
> +/* Secure Encrypted Virtualization */

If anything, this comment should explain what that variable is.
Basically the comment you have in sev_hardware_setup() now.

> +static unsigned int max_sev_asid;
> +
>  static inline void mark_all_dirty(struct vmcb *vmcb)
>  {
>  	vmcb->control.clean = 0;
> @@ -769,7 +772,7 @@ 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);
> @@ -1033,6 +1036,21 @@ static int avic_ga_log_notifier(u32 ga_tag)
>  	return 0;
>  }
>  
> +static __init void sev_hardware_setup(void)
> +{
> +	int nguests;
> +
> +	/*
> +	 * Get maximum number of encrypted guest supported: Fn8001_001F[ECX]
> +	 *     Bit 31:0: Number of supported guest
> +	 */
> +	nguests = cpuid_ecx(0x8000001F);
> +	if (!nguests)
> +		return;
> +
> +	max_sev_asid = nguests;
> +}

max_sev_asid is static and it is already initialized to 0 and thus this
function can be simplified to:

/*
 * Get maximum number of encrypted guest supported: Fn8001_001F[ECX].
 *   [31:0]: Number of supported guests.
 */
static __init void sev_hardware_setup(void)
{
        max_sev_asid = cpuid_ecx(0x8000001F);
}

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--