linux-kernel - Re: [PATCH 1/2] x86/tdx: Add prctl to allow userlevel TDX hypercalls

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Message-ID: <wnd5rlqcus3tnmlaybbxq7v4fkdf2xyv7zhqk4euhbylecff72@evzweah55jis>
Date: Tue, 23 Jul 2024 12:10:55 +0300
From: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
To: Tim Merrifield <tim.merrifield@...adcom.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>, Xin Li <xin3.li@...el.com>, 
	Ard Biesheuvel <ardb@...nel.org>, Kai Huang <kai.huang@...el.com>, 
	Kevin Loughlin <kevinloughlin@...gle.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Kees Cook <kees@...nel.org>, Mike Rapoport <rppt@...nel.org>, 
	Brian Gerst <brgerst@...il.com>, linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Ajay Kaher <ajay.kaher@...adcom.com>, Alexey Makhalov <alexey.makhalov@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, virtualization@...ts.linux.dev, alex.james@...adcom.com, 
	doug.covelli@...adcom.com, jeffrey.sheldon@...adcom.com
Subject: Re: [PATCH 1/2] x86/tdx: Add prctl to allow userlevel TDX hypercalls

On Mon, Jul 22, 2024 at 10:04:40PM -0700, Tim Merrifield wrote:
> 
> Thanks for the review, Kirill.
> 
> On Mon, Jul 08, 2024 at 03:19:54PM +0300, Kirill A . Shutemov wrote:
> > Hm. Per-thread flag is odd. I think it should be per-process.
> 
> This is the only point I might need some clarification on. I agree
> there doesn't seem to be much value in allowing per-thread control,
> but I don't see any precedence for setting per-process flags through
> arch_prctl or similar interfaces. Am I missing something?

LAM is per-process. But it can only be enabled while the process has only
one thread and locks on second thread spawn. See MM_CONTEXT_LOCK_LAM.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov