linux-kernel - Re: [PATCH v6 0/6] x86/tdx: Allow MMIO instructions from userspace

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Message-ID: <c0d9ff5f-85d5-4df0-94a8-82e3bf6fe21f@intel.com>
Date: Fri, 13 Sep 2024 09:01:08 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
 Alexey Gladkov <legion@...nel.org>, linux-kernel@...r.kernel.org,
 linux-coco@...ts.linux.dev, 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>,
 Andrew Morton <akpm@...ux-foundation.org>, Yuan Yao <yuan.yao@...el.com>,
 Geert Uytterhoeven <geert@...ux-m68k.org>, Yuntao Wang <ytcoode@...il.com>,
 Kai Huang <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
 Oleg Nesterov <oleg@...hat.com>, cho@...rosoft.com, decui@...rosoft.com,
 John.Starks@...rosoft.com, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v6 0/6] x86/tdx: Allow MMIO instructions from userspace

On 9/13/24 08:53, Kirill A. Shutemov wrote:
>> Basically:
>>
>> 	New ABI =~ Specific Kernel-mandated Instructions
> If we are going to say "no" to userspace MMIO emulation for TDX, the same
> has to be done for SEV. Or we can bring TDX to SEV level and draw the line
> there.
> 
> SEV and TDX run similar workloads and functional difference in this area
> is hard to justify.

Maybe.  We definitely don't want to put any new restrictions on SEV
because folks would update their kernel and old userspace would break.

Or maybe we start enforcing things at >=SEV-SNP and TDX and just say
that security model has changed too much to allow the old userspace.