linux-kernel - Re: [PATCH v4 4/4] x86/sev: Add SNP-specific unaccepted memory support

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Message-ID: <58903fe7-c4d9-def6-71f4-6173b47fe462@amd.com>
Date:   Fri, 26 Aug 2022 16:29:12 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dionna Amalie Glaze <dionnaglaze@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        "H. Peter Anvin" <hpa@...or.com>,
        Michael Roth <michael.roth@....com>,
        Joerg Roedel <jroedel@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4 4/4] x86/sev: Add SNP-specific unaccepted memory
 support

On 8/25/22 17:10, Dionna Amalie Glaze wrote:
>>
>> Add SNP-specific hooks to the unaccepted memory support in the boot
>> path (__accept_memory()) and the core kernel (accept_memory()) in order
>> to support booting SNP guests when unaccepted memory is present. Without
>> this support, SNP guests will fail to boot and/or panic() when unaccepted
>> memory is present in the EFI memory map.
>>
>> The process of accepting memory under SNP involves invoking the hypervisor
>> to perform a page state change for the page to private memory and then
>> issuing a PVALIDATE instruction to accept the page.
> 
> Thanks for this update! Tests show the boot performance shaves off a
> good few seconds over eager acceptance, and it'll get better when we
> have on-demand pinning.
> 
> The uncaught #VC exception is still there for 256GB machines and larger though.

Any chance of getting a stack trace when this occurs, e.g. adding a 
WARN_ON() in vc_handle_exitcode() (assuming it happens when logging is 
enabled)?

Thanks,
Tom

>