linux-kernel - Re: [PATCH v2 1/2] Add prctl to allow userlevel TDX hypercalls

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Message-ID: <djcj4rubfrjdha64bdea5mvujfbtf2j5lgipywvkkdugbrl5u5@xbg5ofqfp6ix>
Date: Fri, 2 Aug 2024 15:47:17 +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, kevin.christopher@...adcom.com, 
	aravind-as.srinivasan@...adcom.com, ravindra.kumar@...adcom.com
Subject: Re: [PATCH v2 1/2] Add prctl to allow userlevel TDX hypercalls

On Fri, Jul 26, 2024 at 06:58:00PM +0000, Tim Merrifield wrote:
> Add a new process-level prctl option to enable/disable user-level
> hypercalls when running in a confidential VM. Add support for
> checking this flag on VMCALL #VE for TDX and transfer control to
> a hypervisor vendor-specific handler.

We need more context from the cover letter here.

> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index f63f8fd00a91..198431919fd2 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -1042,6 +1042,24 @@ unsigned long __get_wchan(struct task_struct *p)
>  	return addr;
>  }
>  
> +static int get_coco_user_hcall_mode(void)
> +{
> +	return !test_bit(MM_CONTEXT_COCO_USER_HCALL,
> +			&current->mm->context.flags);

Hm. Why "!"?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov