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

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Message-ID: <h5gp6dgcfazm2yk3lorwqms24c2y2z4saqyed6bnzkk2zhq5g2@rf3lj2a22omd>
Date: Thu, 12 Sep 2024 12:45:15 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Dave Hansen <dave.hansen@...el.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 Wed, Sep 11, 2024 at 09:19:04AM -0700, Sean Christopherson wrote:
> Yep.  Based on the original report[*], it sounds like the userspace program is
> doing a memcpy(), so it's hard to even argue that userspace is being silly.

The kernel does MMIO accesses using special helpers that use well-known
instructions. I believe we should educate userspace to do the same by
rejecting emulation of anything more complex than plain loads and stores.
Otherwise these asks will keep coming.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov