linux-kernel - Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver

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Date:   Fri, 4 Mar 2022 09:43:39 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org
Cc:     brijesh.singh@....com, 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>,
        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.shutemov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver


On 3/4/22 9:23 AM, Dave Hansen wrote:
> On 3/4/22 05:17, Brijesh Singh wrote:
>>> BTW, this look like a generic allocator thingy.  But it's only ever used
>>> to allocate a 'struct snp_guest_msg'.  Why all the trouble to allocate
>>> and free one fixed-size structure?  The changelog and comments don't
>>> shed any light.
>> The GHCB specification says that a guest must use shared memory for
>> request, response, and certificate blob. In this patch, you are seeing
>> that {alloc,free}_shared_pages() used only to alloc/free the request and
>> response page. In the last patch, we used the same generic function to
>> allocate the certificate blob with a different size (~16K) than 'struct
>> snp_guest_msg.'
> It sounds like it's worth a sentence or two in the changelog to explain
> this new "allocator" and its future uses.

Will do.