linux-kernel - Re: [PATCH v2 RESEND] x86/asm: Force native_apic_mem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <e74b4fe3-1233-3fea-4a2b-1d5e344d9a40@amd.com>
Date:   Thu, 15 Sep 2022 02:51:58 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Marc Orr <marcorr@...gle.com>, Peter Gonda <pgonda@...gle.com>
Cc:     Adam Dunlap <acdunlap@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ben Dooks <ben-linux@...ff.org>,
        LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev,
        Jacob Xu <jacobhxu@...gle.com>, Alper Gun <alpergun@...gle.com>
Subject: Re: [PATCH v2 RESEND] x86/asm: Force native_apic_mem_read to use mov

On 9/14/22 06:59, Marc Orr wrote:
> On Wed, Sep 14, 2022 at 12:59 PM Marc Orr <marcorr@...gle.com> wrote:
>>
>> On Wed, Sep 14, 2022 at 12:13 PM Peter Gonda <pgonda@...gle.com> wrote:
>>>
>>> On Thu, Sep 8, 2022 at 6:05 PM Adam Dunlap <acdunlap@...gle.com> wrote:
>>>>
>>>> Previously, when compiled with clang, native_apic_mem_read gets inlined
>>>> into __xapic_wait_icr_idle and optimized to a testl instruction. When
>>>> run in a VM with SEV-ES enabled, it attempts to emulate this
>>>> instruction, but the emulator does not support it. Instead, use inline
>>>> assembly to force native_apic_mem_read to use the mov instruction which
>>>> is supported by the emulator.
>>>
>>> This seems to be an issue with the SEV-ES in guest #VC handler's
>>> "emulator" right?
>>>
>>> If that's the case I think this should be fixed in the #VC handler
>>> instead of fixing the code that is failing to be emulated. What if
>>> there are other places where a testl is used and our tests have not
>>> caught them.
>>
>> That was my initial reaction too. But we spoke w/ Tom offline (before
>> sending this) and my understanding was that we really should be using
>> MOV for MMIO. I've cc'd Tom so he can speak to this directly though.

I did finally find the section in our PPR that references using the MOV 
instruction, but it was for MMIO configuration space, not general MMIO 
operations.

So, yes, the #VC handler could be extended to handle a TEST instruction to 
fix this. My worry would be if the compiler decided to use a different 
instruction in the future. I see that the native_apic_mem_write() is using 
assembler to perform its operation, it just seemed right that the 
native_apic_mem_read() could do the same.

Thanks,
Tom

> 
> Actually cc'ing Tom :-).