Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220812183501.3555820-1-acdunlap@google.com> <20220908170456.3177635-1-acdunlap@google.com>
 <CAMkAt6qUs526FCq26Ht48c2KVZWe=QcNds6_LE6JJbs-7Hzk+g@mail.gmail.com>
 <2625dbfa-434c-7d55-6469-9d9e89397e8f@intel.com> <YyH/tOqrl8pZmoub@google.com>
 <CAMkAt6p2Y=6sBB1JiZ2FovYXme9QBFWFu+EtnNyuQ3Db3ZhBSg@mail.gmail.com>
 <CAMBK9=YB=8EQymDUda300qPFAL1=7dzC61c0pshrWEC5ibrUfQ@mail.gmail.com>
 <B7175642-351D-44A0-B7AD-E69C6B64FC18@zytor.com> <81950d38-4d5a-6902-bc2e-327d2800eb58@amd.com>
In-Reply-To: <81950d38-4d5a-6902-bc2e-327d2800eb58@amd.com>
From:   Marc Orr <marcorr@google.com>
Date:   Thu, 17 Nov 2022 13:23:08 -0800
Message-ID: <CAA03e5Gb0BDn-e7Th8JPQqrX-EmFW3kGeiKfuFvwEzKe6xRadg@mail.gmail.com>
Subject: Re: [PATCH v2 RESEND] x86/asm: Force native_apic_mem_read to use mov
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     "H. Peter Anvin" <hpa@zytor.com>,
        Adam Dunlap <acdunlap@google.com>,
        Peter Gonda <pgonda@google.com>,
        Sean Christopherson <seanjc@google.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Ben Dooks <ben-linux@fluff.org>,
        LKML <linux-kernel@vger.kernel.org>, llvm@lists.linux.dev,
        Jacob Xu <jacobhxu@google.com>, Alper Gun <alpergun@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Oct 5, 2022 at 6:29 AM Tom Lendacky <thomas.lendacky@amd.com> wrote:
>
> On 10/3/22 18:11, H. Peter Anvin wrote:
> > On October 3, 2022 4:01:01 PM PDT, Adam Dunlap <acdunlap@google.com> wrote:
> >> Thanks for all the responses. Is the consensus that we should use the
> >> readl function here or instead use inline assembly directly as in the patch
> >> I originally sent out:
> >>
> >> asm_inline("movl %1, %0" : "=r"(out) : "m"(*addr));
> >>
> >> ? The readl function has this exact same code, I'm just not sure
> >> which version fits better stylistically.
> >
> > Is mov with an arbitrary addressing mode still acceptable for whatever is causing this problem?
>
> The acceptable forms of MOV are covered by insn_decode_mmio() in
> arch/x86/lib/insn-eval.c.

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/

Thanks,
Marc