linux-kernel - Re: [PATCH Part2 v5 21/45] KVM: SVM: Make AVIC backing, VMSA and VMCB memory allocation SNP safe

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Date:   Thu, 23 Sep 2021 13:55:00 -0700
From:   Marc Orr <marcorr@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>, linux-coco@...ts.linux.dev,
        linux-mm@...ck.org, linux-crypto@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part2 v5 21/45] KVM: SVM: Make AVIC backing, VMSA and VMCB
 memory allocation SNP safe

On Thu, Sep 23, 2021 at 1:44 PM Brijesh Singh <brijesh.singh@....com> wrote:
>
>
> On 9/23/21 2:17 PM, Marc Orr wrote:
>
> >>>> +
> >>>> +struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu)
> >>>> +{
> >>>> +    unsigned long pfn;
> >>>> +    struct page *p;
> >>>> +
> >>>> +    if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> >>>> +            return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
> > Continuing my other comment, above: if we introduce a
> > `snp_globally_enabled` var, we could use that here, rather than
> > `cpu_feature_enabled(X86_FEATURE_SEV_SNP)`.
>
>
> Maybe I am missing something, what is wrong with
> cpu_feature_enabled(...) check ? It's same as creating a global
> variable. The feature enabled bit is not set if the said is not
> enabled.  See the patch #3 [1] in this series.
>
> [1]
> https://lore.kernel.org/linux-mm/YUN+L0dlFMbC3bd4@zn.tnic/T/#m2ac1242b33abfcd0d9fb22a89f4c103eacf67ea7
>
> thanks

You are right. Patch #3 does exactly what I was asking for in
`snp_rmptable_init()`. Thanks!