linux-kernel - Re: [PATCH 26/26] KVM: x86: asi: Add some mitigations on address space transitions

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Message-ID: <bcdc6114-2a31-4f68-a066-fae8eed3833b@amd.com>
Date: Wed, 21 Aug 2024 21:30:18 +0530
From: Shivank Garg <shivankg@....com>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>, Alexandre Chartre <alexandre.chartre@...cle.com>,
 Liran Alon <liran.alon@...cle.com>,
 Jan Setje-Eilers <jan.setjeeilers@...cle.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>,
 Lorenzo Stoakes <lstoakes@...il.com>, David Hildenbrand <david@...hat.com>,
 Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
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 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Valentin Schneider <vschneid@...hat.com>, Paul Turner <pjt@...gle.com>,
 Reiji Watanabe <reijiw@...gle.com>, Junaid Shahid <junaids@...gle.com>,
 Ofir Weisse <oweisse@...gle.com>, Yosry Ahmed <yosryahmed@...gle.com>,
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 Alexandra Sandulescu <aesa@...gle.com>, Matteo Rizzo
 <matteorizzo@...gle.com>, Jann Horn <jannh@...gle.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, kvm@...r.kernel.org
Subject: Re: [PATCH 26/26] KVM: x86: asi: Add some mitigations on address
 space transitions

Hi Brendan,

On 8/21/2024 3:08 PM, Brendan Jackman wrote:
> Hi Shivank,
> 
> On Tue, 20 Aug 2024 at 11:52, Shivank Garg <shivankg@....com> wrote:
>>
>>  .pushsection .noinstr.text, "ax"
>>  SYM_CODE_START(fill_return_buffer)
>> +       UNWIND_HINT_FUNC
>>         __FILL_RETURN_BUFFER(%_ASM_AX,RSB_CLEAR_LOOPS)
>>         RET
>>  SYM_CODE_END(fill_return_buffer)
>> +__EXPORT_THUNK(fill_return_buffer)
>>  .popsection
> 
> Thanks a lot for the pointer! UNWIND_HINT_FUNC does indeed seem to be
> what I was missing with the objtool warning.
> 
> Regarding the build failure, could you share your config/toolchain
> info so I can try to reproduce? Would be handy for checking my next
> posting. Now I see your mail, it seems surprising that it compiles for
> me.
>
gcc --version
gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0

I have attached my config.

> Also while I'm replying to this thread I'll note this:
> 
>> +       if (!IS_ENABLED(CONFIG_RETPOLINE) ||
>> +           !cpu_feature_enabled(X86_FEATURE_RSB_VMEXIT))
> 
> It's called CONFIG_MITIGATION_RETPOLINE now.
> 
> And furthermore, kvm_get_running_vcpu needs to be noinstr, I'm getting
> an objtool warning about this that wasn't mentioned in my cover
> letter.
Strangely, I didn't see this warning.

Thanks,
Shivank
View attachment ".config" of type "text/plain" (184516 bytes)