linux-kernel - RE: [EXTERNAL] Re: [PATCH] x86/tdx: Generate SIGBUS on userspace MMIO

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Date: Thu, 23 May 2024 17:08:40 +0000
From: Chris Oo <cho@...rosoft.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Kuppuswamy
 Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
CC: Dave Hansen <dave.hansen@...ux.intel.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>, "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Dexuan Cui
	<decui@...rosoft.com>, John Starks <John.Starks@...rosoft.com>
Subject: RE: [EXTERNAL] Re: [PATCH] x86/tdx: Generate SIGBUS on userspace MMIO

We use this to handle MMIO issued by userspace that the kernel does not handle in a #VE, for devices assigned to a TDX VM. 

Chris

-----Original Message-----
From: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> 
Sent: Thursday, May 23, 2024 3:15 AM
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>; Thomas Gleixner <tglx@...utronix.de>; Ingo Molnar <mingo@...hat.com>; Borislav Petkov <bp@...en8.de>; x86@...nel.org; H. Peter Anvin <hpa@...or.com>; linux-coco@...ts.linux.dev; linux-kernel@...r.kernel.org; Chris Oo <cho@...rosoft.com>; Dexuan Cui <decui@...rosoft.com>; John Starks <John.Starks@...rosoft.com>
Subject: [EXTERNAL] Re: [PATCH] x86/tdx: Generate SIGBUS on userspace MMIO

On Tue, May 21, 2024 at 06:35:49AM -0700, Kuppuswamy Sathyanarayanan wrote:
> 
> On 5/21/24 12:35 AM, Kirill A. Shutemov wrote:
> > Currently attempt to do MMIO from userspace in TDX guest leads to 
> > warning about unexpect #VE and SIGSEGV being delivered to the process.
> >
> > Enlightened userspace might choose to deal with MMIO on their own if 
> > kernel doesn't emulate it.
> 
> Any specific use cases ? Like who is using it?

Microsoft folks wanted it. Chris, Dexuan, John, any comments?

But it is generally right thing to do. SIGBUS is right signal to deliver.

--
  Kiryl Shutsemau / Kirill A. Shutemov