Cc:     brijesh.singh@amd.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
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        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section
 shared in RMP table
To:     Dave Hansen <dave.hansen@intel.com>,
        Venu Busireddy <venu.busireddy@oracle.com>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-14-brijesh.singh@amd.com> <YdSKQKSTS83cRzGZ@dt>
 <18eadf9d-8e31-0945-ccf4-2cb72b8e0dd4@amd.com>
 <acba0832-9b11-c93d-7903-fff33f740605@intel.com>
From:   Brijesh Singh <brijesh.singh@amd.com>
Message-ID: <444b6c78-c4d3-f49c-6579-bd28ae32ca3c@amd.com>
Date:   Wed, 5 Jan 2022 15:39:22 -0600
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On 1/5/22 2:27 PM, Dave Hansen wrote:
> On 1/5/22 11:52, Brijesh Singh wrote:
>>>>           for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
>>>> +            /*
>>>> +             * When SEV-SNP is active then transition the page to 
>>>> shared in the RMP
>>>> +             * table so that it is consistent with the page table 
>>>> attribute change.
>>>> +             */
>>>> +            early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), 
>>>> PTRS_PER_PMD);
>>>
>>> Shouldn't the first argument be vaddr as below?
>>
>> Nope, sme_postprocess_startup() is called while we are fixing the 
>> initial page table and running with identity mapping (so va == pa).
> 
> I'm not sure I've ever seen a line of code that wanted a comment so badly.

The early_snp_set_memory_shared() call the PVALIDATE instruction to 
clear the validated bit from the BSS region. The PVALIDATE instruction 
needs a virtual address, so we need to use the identity mapped virtual 
address so that PVALIDATE can clear the validated bit. I will add more 
comments to clarify it.

-Brijesh