linux-kernel - Re: [PATCHv5 3/4] x86/tdx: Dynamically disable SEPT violations from causing #VEs

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Message-ID: <auyvnefisebmpfj3ugj76qagqmrd6xstxv36otmd5az2smdskk@dw74rg3tqw73>
Date: Wed, 3 Jul 2024 16:05:32 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Nikolay Borisov <nik.borisov@...e.com>, g@...ck.fi.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, stable@...r.kernel.orgg
Subject: Re: [PATCHv5 3/4] x86/tdx: Dynamically disable SEPT violations from
 causing #VEs

On Wed, Jul 03, 2024 at 03:22:35PM +0300, Nikolay Borisov wrote:
> 
> 
> On 24.06.24 г. 14:41 ч., Kirill A. Shutemov wrote:
> 
> <snip>
> 
> 
> 
> > --- a/arch/x86/include/asm/shared/tdx.h
> > +++ b/arch/x86/include/asm/shared/tdx.h
> > @@ -19,9 +19,17 @@
> >   #define TDG_VM_RD			7
> >   #define TDG_VM_WR			8
> > -/* TDCS fields. To be used by TDG.VM.WR and TDG.VM.RD module calls */
> > +/* TDX TD-Scope Metadata. To be used by TDG.VM.WR and TDG.VM.RD */
> > +#define TDCS_CONFIG_FLAGS		0x1110000300000016
> > +#define TDCS_TD_CTLS			0x1110000300000017
> >   #define TDCS_NOTIFY_ENABLES		0x9100000000000010
> > +/* TDCS_CONFIG_FLAGS bits */
> > +#define TDCS_CONFIG_FLEXIBLE_PENDING_VE	BIT_ULL(1)
> 
> 
> So where is this bit documented, because in td_scope_metadata.json
> CONFIG_FLAGS' individual bits aren't documented. All other TDX docs refer to
> the ABI .json file.
> 
> Landing code for undocumented bits unfortunately precludes any quality
> review on behalf of independent parties.
> 
> > +
> > +/* TDCS_TD_CTLS bits */
> > +#define TD_CTLS_PENDING_VE_DISABLE	BIT_ULL(0)
> 
> In contrast the TD_CTLS bits are documented in the same .json file.

Yes, TDX documentation is lacking here. I hope it will be fixed in the
next version.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov