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Date:   Tue, 4 Apr 2023 10:57:52 -0700
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Subject: Re: [PATCH v7 6/6] x86/efi: Safely enable unaccepted memory in UEFI
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To:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Tom Lendacky <thomas.lendacky@amd.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        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>,
        Michael Roth <michael.roth@amd.com>,
        Joerg Roedel <jroedel@suse.de>,
        Dionna Glaze <dionnaglaze@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ard Biescheuvel <ardb@kernel.org>,
        "Min M. Xu" <min.m.xu@intel.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        James Bottomley <jejb@linux.ibm.com>,
        Jiewen Yao <jiewen.yao@intel.com>,
        Erdem Aktas <erdemaktas@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20230330114956.20342-1-kirill.shutemov@linux.intel.com>
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 <20230404174506.pjdikxvk2fsyy4au@box.shutemov.name>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230404174506.pjdikxvk2fsyy4au@box.shutemov.name>
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On 4/4/23 10:45, Kirill A. Shutemov wrote:
> I still think it is a bad idea.
> 
> As I asked before, please include my
> 
> Nacked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 
> into the patch.

I was pretty opposed to this when I first saw it too.  But, Tom and
company have worn down my opposition a bit.

The fact is that we have upstream kernels out there with SEV-SNP support
that don't know anything about unaccepted memory.  They're either
relegated to using the pre-accepted memory (4GB??) or _some_ entity
needs to accept the memory.  That entity obviously can't be the kernel
unless we backport unaccepted memory support.

This both lets the BIOS be the page-accepting entity _and_ allows the
entity to delegate that to the kernel when it needs to.

As much as I want to nak this and pretend that that those existing
kernel's don't exist, my powers of self-delusion do have their limits.

If our AMD friends don't do this, what is their alternative?