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;
Message-ID: <ab569bc4-df47-819a-4a72-1e1ab696f9b2@intel.com>
Date:   Wed, 12 Apr 2023 07:35:20 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [RFC PATCH] x86/fpu/xstate: Add more diagnostic information on
 inconsistent xstate sizes
Content-Language: en-US
To:     Fenghua Yu <fenghua.yu@intel.com>,
        "Chang S. Bae" <chang.seok.bae@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
        Chintan M Patel <chintan.m.patel@intel.com>,
        Thiago Macieira <thiago.macieira@intel.com>
References: <20230405183942.734019-1-fenghua.yu@intel.com>
 <113918f9-0e44-3d46-8b48-028277ec26bb@intel.com>
 <c716e021-99ad-2cb7-44c0-ec8393a3440d@intel.com>
 <2af114b9-2737-70e5-f534-e60416b52246@intel.com>
 <50e67263-33ba-9921-1bc2-a37b99bc2459@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <50e67263-33ba-9921-1bc2-a37b99bc2459@intel.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 4/11/23 18:21, Fenghua Yu wrote:
> In other words, splitting max_features into XCR0 and IA32_XSS and
> showing them individually provide more useful debug info than one single
> max_features value.
> 
> Does it make sense?

Not to me.

>> I still expect some acknowledgment of what is coded here for the
>> kernel calculation details.
> 
> The kernel calculation is shown in
> +        print_xstate_offset_size();
> +        pr_info("x86/fpu: total size: %u bytes\n", size);
> 
> Isn't that detailed enough to show offset and size of each xstate and
> sum of sizes?
> 
> After that,
> +    pr_info("x86/fpu: kernel_size from CPUID.0xd.0x%x:EBX: %u bytes\n",
> +               compacted ? 1 : 0, kernel_size);
> shows how kernel_size is calculated from CPUID?
> 
> Using the above debug info, a real platform CPUID issue is shown clearly.
> 
> What other details are needed?

I was kinda hoping this would be a simple, non-controversial patch that
would get us better debugging info the next time that the microcode or a
bad VMM screws up.  This patch isn't turning out to be as simple as I hoped.

I was wrong.  Let's just drop this.