linux-kernel - Re: [PATCH Part1 RFC v3 05/22] x86/sev: Add support for hypervisor feature VMGEXIT

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Date:   Mon, 7 Jun 2021 09:58:30 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....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,
        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>, tony.luck@...el.com,
        npmccallum@...hat.com
Subject: Re: [PATCH Part1 RFC v3 05/22] x86/sev: Add support for hypervisor
 feature VMGEXIT


On 6/7/21 9:19 AM, Borislav Petkov wrote:
> On Wed, Jun 02, 2021 at 09:03:59AM -0500, Brijesh Singh wrote:
>> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
>> index 70f181f20d92..94957c5bdb51 100644
>> --- a/arch/x86/kernel/sev-shared.c
>> +++ b/arch/x86/kernel/sev-shared.c
> I'm guessing this is in sev-shared.c because it is going to be used by
> both stages?

Yes,  the function is used by both the stages.


>> @@ -20,6 +20,7 @@
>>   * out when the .bss section is later cleared.
>>   */
>>  static u16 ghcb_version __section(".data");
> State what this is:
>
> /* Bitmap of SEV features supported by the hypervisor */

Noted.


>
>> +static u64 hv_features __section(".data");
> Also, I'm assuming that bitmap remains immutable during the guest
> lifetime so you can do:
>
> static u64 hv_features __ro_after_init;
>
> instead, which will do:
>
> static u64 hv_features __attribute__((__section__(".data..ro_after_init")));
>
> and it'll be in the data section and then also marked read-only after
> init, after mark_rodata_ro() more specifically.

Yes, it should be immutable. I will set the ro_after_init section to
mark it read-only. thanks