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Message-ID: <cc90c896-7581-62b5-4836-971e9ca8fac0@intel.com>
Date: Fri, 8 Sep 2023 07:48:58 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Tom Lendacky <thomas.lendacky@....com>,
Adam Dunlap <acdunlap@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
David Hildenbrand <david@...hat.com>,
Mike Rapoport <rppt@...nel.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Nikunj A Dadhania <nikunj@....com>,
Dionna Glaze <dionnaglaze@...gle.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Joerg Roedel <jroedel@...e.de>, Jacob Xu <jacobhxu@...gle.com>
Subject: Re: [PATCH] x86/sev-es: Do not use copy_from_kernel_nofault in early
#VC handler
On 9/8/23 06:13, Tom Lendacky wrote:
> On 9/7/23 14:12, Dave Hansen wrote:
>> But seriously, is it even *possible* to spin up a SEV-SNP VM what
>> doesn't have NX?
>
> It is a common path, so while an SEV guest would have NX support, you
> would first have to determine that it is an SEV guest. That would take
> issuing a CPUID instruction in order to determine if a particular MSR
> can be read...
I was thinking more along the lines of telling folks that if they want
to turn SEV-SNP support on, they also have to give up on running on a
!NX system. That would be a _bit_ nicer than just refusing to boot on
all !NX systems.
> Ultimately, we could probably pass the encryption mask from the
> decompressor to the kernel and avoid some of the checks during early
> boot of the kernel proper. Is it possible to boot an x86 kernel without
> going through the decompressor?
I think it's possible, but it's very unusual.
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