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From:   Paul Durrant <xadimgnik@gmail.com>
Message-ID: <5b448307-19f3-4d69-b7f4-3ebedcff030a@xen.org>
Date:   Tue, 26 Sep 2023 10:22:07 +0100
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Reply-To: paul@xen.org
Subject: Re: [PATCH v5 06/10] KVM: xen: allow shared_info to be mapped by
 fixed HVA
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To:     David Woodhouse <dwmw2@infradead.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Paul Durrant <pdurrant@amazon.com>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
References: <20230922150009.3319-1-paul@xen.org>
 <20230922150009.3319-7-paul@xen.org>
 <0bd42244f232ecc24cbbd2750196758bf7944293.camel@infradead.org>
Organization: Xen Project
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On 23/09/2023 08:07, David Woodhouse wrote:
> On Fri, 2023-09-22 at 15:00 +0000, Paul Durrant wrote:
>> From: Paul Durrant <pdurrant@amazon.com>
>>
>> The shared_info page is not guest memory as such. It is a dedicated page
>> allocated by the VMM and overlaid onto guest memory in a GFN chosen by the
>> guest. The guest may even request that shared_info be moved from one GFN
>> to another, but the HVA is never going to change. Thus it makes much more
>> sense to map the shared_info page in kernel once using this fixed HVA.
> 
> The words "makes much more sense" are doing a *lot* of work there. :)
> 
> When heckling the cover letter in
> https://lore.kernel.org/kvm/d13e459e221f28fb1865eedea023e583a2277ab1.camel@infradead.org/
> I suggested that the explanation probably wants to make it into a
> commit message rather than just the cover letter which tends not to be
> preserved in the commit history. It's *this* commit which needs it, I
> think.

Ok, I'll try to come up with some concise wording.

   Paul