linux-kernel - Re: [PATCH v4 6/6] x86/tdx: Implement movs for MMIO

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Message-ID: <tcngnuglju2mnpfa4o2hw3fpwdkk4ryso5dq2zjfi2wn4yr5yd@2iij74o7ugaf>
Date: Thu, 22 Aug 2024 11:28:14 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Alexey Gladkov <legion@...nel.org>
Cc: 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
Subject: Re: [PATCH v4 6/6] x86/tdx: Implement movs for MMIO

On Wed, Aug 21, 2024 at 04:24:38PM +0200, Alexey Gladkov wrote:
> From: "Alexey Gladkov (Intel)" <legion@...nel.org>
> 

Please capitalize MOVS in the subject.

> Add emulation of the MOVS instruction on MMIO regions. MOVS emulation
> consists of dividing it into a series of read and write operations,
> which in turn will be validated separately.

Commit message is pretty sparse. I think we need to elaborate on the
similarities and differences with SEV implementation. Locking context
difference is important.

> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index a75a07f4931f..45136b1b02cc 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -503,6 +503,10 @@ struct thread_struct {
>  	struct thread_shstk	shstk;
>  #endif
>  
> +#ifdef CONFIG_INTEL_TDX_GUEST
> +	unsigned long		mmio_emul;
> +#endif
> +
>  	/* Floating point and extended processor state */
>  	struct fpu		fpu;
>  	/*

Hm. Do we need to track exact target address in the thread struct?
Wouldn't be single bit be enough to allow MMIO to userspace address from a
kernel regs->ip?

There is space for the flag next to iopl_warn.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov