Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:3 as permitted sender) client-ip=2620:137:e000::3:3;
Message-ID: <5cf50d76-8e18-2863-4889-70e9c18298a1@zytor.com>
Date:   Thu, 14 Sep 2023 17:38:57 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.13.0
Subject: Re: [PATCH v10 03/38] x86/msr: Add the WRMSRNS instruction support
Content-Language: en-US
To:     andrew.cooper3@citrix.com, Thomas Gleixner <tglx@linutronix.de>,
        Xin Li <xin3.li@intel.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
        linux-hyperv@vger.kernel.org, kvm@vger.kernel.org,
        xen-devel@lists.xenproject.org
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        x86@kernel.org, luto@kernel.org, pbonzini@redhat.com,
        seanjc@google.com, peterz@infradead.org, jgross@suse.com,
        ravi.v.shankar@intel.com, mhiramat@kernel.org,
        jiangshanlai@gmail.com
References: <20230914044805.301390-1-xin3.li@intel.com>
 <20230914044805.301390-4-xin3.li@intel.com>
 <6f5678ff-f8b1-9ada-c8c7-f32cfb77263a@citrix.com> <87y1h81ht4.ffs@tglx>
 <7ba4ae3e-f75d-66a8-7669-b6eb17c1aa1c@citrix.com> <87v8cc1ehe.ffs@tglx>
 <50e96f85-66f8-2a4f-45c9-a685c757bb28@citrix.com>
From:   "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <50e96f85-66f8-2a4f-45c9-a685c757bb28@citrix.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 9/14/23 17:33, andrew.cooper3@citrix.com wrote:
> 
> It's an assumption about what "definitely won't" be paravirt in the future.
> 
> XenPV stack handling is almost-FRED-like and has been for the better
> part of two decades.
> 
> You frequently complain that there's too much black magic holding XenPV
> together.  A paravirt-FRED will reduce the differences vs native
> substantially.
> 

Call it "paravirtualized exception handling." In that sense, the 
refactoring of the exception handling to benefit FRED is definitely 
useful for reducing paravirtualization. The FRED-specific code is 
largely trivial, and presumably what you would do is to replace the FRED 
wrapper with a Xen wrapper and call the common handler routines.

	-hpa