linux-kernel - Re: [PATCH v2] KVM: x86: Assume a 64-bit hypercall for guests with protected state

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Date:   Thu, 11 Nov 2021 14:46:03 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>,
        Ashish Kalra <Ashish.Kalra@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        kvm list <kvm@...r.kernel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH v2] KVM: x86: Assume a 64-bit hypercall for guests with
 protected state

On 10/26/21 1:03 PM, Tom Lendacky wrote:
> On 10/1/21 12:06 PM, Tom Lendacky wrote:
>> On 5/25/21 1:25 AM, Vitaly Kuznetsov wrote:
>>> Tom Lendacky <thomas.lendacky@....com> writes:
>>>
>>>> When processing a hypercall for a guest with protected state, currently
>>>> SEV-ES guests, the guest CS segment register can't be checked to
>>>> determine if the guest is in 64-bit mode. For an SEV-ES guest, it is
>>>> expected that communication between the guest and the hypervisor is
>>>> performed to shared memory using the GHCB. In order to use the GHCB, the
>>>> guest must have been in long mode, otherwise writes by the guest to the
>>>> GHCB would be encrypted and not be able to be comprehended by the
>>>> hypervisor.
>>>>
>>>> Create a new helper function, is_64_bit_hypercall(), that assumes the
>>>> guest is in 64-bit mode when the guest has protected state, and returns
>>>> true, otherwise invoking is_64_bit_mode() to determine the mode. Update
>>>> the hypercall related routines to use is_64_bit_hypercall() instead of
>>>> is_64_bit_mode().
>>>>
>>>> Add a WARN_ON_ONCE() to is_64_bit_mode() to catch occurences of calls to
>>>> this helper function for a guest running with protected state.
>>>>
>>>> Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support 
>>>> intercepts under SEV-ES")
>>>> Reported-by: Sean Christopherson <seanjc@...gle.com>
>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>>>> ---

...

>>>
>>> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>>>
>>> Thanks!
>>
>> Paolo,
>>
>> This got lost in my stack of work... any comments?
>>
>> Thanks,
>> Tom
> 
> Ping
> 
> Thanks,
> Tom

Another ping on this.

Paolo, you had replied "queued" on the v1, but came up with a suggestion
for a v2 that might have got lost in the replies because it never got
queued. Here are the threads:

v1: https://lore.kernel.org/kvm/d0904f0d049300267665bd4abf96c3d7e7aa4825.1621701837.git.thomas.lendacky@amd.com/

v2: https://lore.kernel.org/kvm/e0b20c770c9d0d1403f23d83e785385104211f74.1621878537.git.thomas.lendacky@amd.com/

Thanks,
Tom

> 
>>
>>>