linux-kernel - Re: [PATCH Part2 v5 05/45] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction

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Date:   Fri, 15 Oct 2021 15:36:13 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, 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>,
        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,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part2 v5 05/45] x86/sev: Add helper functions for
 RMPUPDATE and PSMASH instruction


On 10/15/21 3:27 PM, Sean Christopherson wrote:
> On Fri, Oct 15, 2021, Brijesh Singh wrote:
>> On 10/15/21 1:05 PM, Sean Christopherson wrote:
>>> On Fri, Aug 20, 2021, Brijesh Singh wrote:
>>>> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
>>> Shouldn't this be a WARN_ON_ONCE()?
>> Since some of these function are called while handling the PSC so I
>> tried to avoid using the WARN -- mainly because if the warn_on_panic=1
>> is set on the host then it will result in the kernel panic.
> But why would KVM be handling PSC requests if SNP is disabled?

The RMPUPDATE is also used by the CCP drv to change the page state
during the initialization. You are right that neither KVM nor CCP should
be using these function when SNP is not enabled. In your peudo code you
used the WARN_ON_ONCE() for the cpu_feature_enabled() and return code
check. I was more concern about the return code WARN_ON_ONCE() because
that will be called during the PSC. I am okay with using the
WARN_ON_ONCE() for the cpu_feature_enabled() check.

thanks