Received-SPF: pass (google.com: domain of linux-kernel+bounces-25840-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Mon, 15 Jan 2024 13:00:11 +0300
From: "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>
To: Michael Kelley <mhklinux@outlook.com>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
	"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"Lutomirski, Andy" <luto@kernel.org>,
	"hch@infradead.org" <hch@infradead.org>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
	"haiyangz@microsoft.com" <haiyangz@microsoft.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"seanjc@google.com" <seanjc@google.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"Cui, Dexuan" <decui@microsoft.com>,
	"urezki@gmail.com" <urezki@gmail.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"hpa@zytor.com" <hpa@zytor.com>, "bp@alien8.de" <bp@alien8.de>,
	"wei.liu@kernel.org" <wei.liu@kernel.org>,
	"Rodel, Jorg" <jroedel@suse.de>,
	"sathyanarayanan.kuppuswamy@linux.intel.com" <sathyanarayanan.kuppuswamy@linux.intel.com>,
	"lstoakes@gmail.com" <lstoakes@gmail.com>,
	"x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH v3 1/3] x86/hyperv: Use slow_virt_to_phys() in page
 transition hypervisor callback
Message-ID: <20240115100011.yvecjjezrkcptnle@box.shutemov.name>
References: <20240105183025.225972-1-mhklinux@outlook.com>
 <20240105183025.225972-2-mhklinux@outlook.com>
 <9dcdd088494b3fa285781cccfd35cd47a70d69c3.camel@intel.com>
 <SN6PR02MB4157B123128F6C2F6C3600D9D46F2@SN6PR02MB4157.namprd02.prod.outlook.com>
 <3ddc237d9fbbe0aa8838babf0df790076017e9f7.camel@intel.com>
 <SN6PR02MB415720444A3D848D444BB58AD46F2@SN6PR02MB4157.namprd02.prod.outlook.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <SN6PR02MB415720444A3D848D444BB58AD46F2@SN6PR02MB4157.namprd02.prod.outlook.com>

On Fri, Jan 12, 2024 at 07:24:35PM +0000, Michael Kelley wrote:
> From: Edgecombe, Rick P <rick.p.edgecombe@intel.com> Sent: Friday, January 12, 2024 9:17 AM
> > 
> > On Fri, 2024-01-12 at 15:07 +0000, Michael Kelley wrote:
> > > The comment is Kirill Shutemov's suggestion based on comments in
> > > an earlier version of the patch series.? See [1].?? The intent is to
> > > prevent
> > > some later revision to slow_virt_to_phys() from adding a check for
> > > the
> > > present bit and breaking the CoCo VM hypervisor callback.? Yes, the
> > > comment could get stale, but I'm not sure how else to call out the
> > > implicit dependency.? The idea of creating a private version of
> > > slow_virt_to_phys() for use only in the CoCo VM hypervisor callback
> > > is also discussed in the thread, but that seems worse overall.
> > 
> > Well, it's not a huge deal, but I would have just put a comment at the
> > caller like:
> > 
> > /*
> >  * Use slow_virt_to_phys() instead of vmalloc_to_page(), because it
> >  * returns the PFN even for NP PTEs.
> >  */
> 
> Yes, that comment is added in this patch.
> 
> > 
> > If someone is changing slow_virt_to_phys() they should check the
> > callers to make sure they won't break anything. They can see the
> > comment then and have an easy time.
> > 
> > An optional comment at slow_virt_to_phys() could explain how the
> > function works in regards to the present bit, but not include details
> > about CoCoO VM page transition's usage of the present bit. The proposed
> > comment text looks like something more appropriate for a commit log.
> 
> Kirill -- you originally asked for a comment in slow_virt_to_phys(). [1]
> Are you OK with Rick's proposal?

Yes, sounds sensible.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov