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

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Message-ID: <daba8825-9c81-4a82-9a7b-a6ea3e2c5537@intel.com>
Date:   Fri, 17 Nov 2023 11:23:47 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sidharth Telang <sidtelang@...gle.com>, marcorr@...gle.com
Cc:     acdunlap@...gle.com, ak@...ux.intel.com, alpergun@...gle.com,
        ben-linux@...ff.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, jacobhxu@...gle.com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, mingo@...hat.com, nathan@...nel.org,
        ndesaulniers@...gle.com, pgonda@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
        tglx@...utronix.de, thomas.lendacky@....com, trix@...hat.com,
        x86@...nel.org
Subject: Re: [PATCH v2 RESEND] x86/asm: Force native_apic_mem_read to use mov

On 11/17/23 10:14, Sidharth Telang wrote:
>> Is this blocked on an item? There seems to be consensus that this
>> patch fixes a bug and is taking the right high-level approach (i.e.,
>> change the guest code to avoid triggering a sequence that isn't
>> supported under CVM exception-based emulation). Without something like
>> this, we weren't able to build the kernel w/ CLANG when it is
>> configured to run under SEV-ES.
> 
>> We sent out two versions of the patch. One that does the mov directly
>> [1] and a second that calls readl [2]. Is one of these two patches
>> acceptable? Or do we need to follow up on something?
>>
>> [1] https://lore.kernel.org/lkml/0D6A1E49-F21B-42AA-BBBF-13BFC308BB1E@zytor.com/T/
>> [2] https://lore.kernel.org/all/20220812183501.3555820-1-acdunlap@google.com/
> 
> Signal-boosting this thread: is this blocked on any item?

Yes, it's blocked on you sending a well-described patch.

You sent out two patches which both received a lot of discussion and
induced a lot of confusion.  Can you please take all the knowledge from
this thread and send a third patch that has a proper changelog
incorporating all that knowledge?

Which approach should that patch have?  Whatever one is as close to what
native_apic_mem_write() does as possible.