linux-kernel - Re: [PATCHv2.1 08/29] x86/tdx: Handle in-kernel MMIO

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Date:   Tue, 1 Feb 2022 17:14:05 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     dave.hansen@...el.com, jpoimboe@...hat.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, knsathya@...nel.org, linux-kernel@...r.kernel.org,
        luto@...nel.org, mingo@...hat.com, pbonzini@...hat.com,
        peterz@...radead.org, sathyanarayanan.kuppuswamy@...ux.intel.com,
        sdeep@...are.com, seanjc@...gle.com, tglx@...utronix.de,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org
Subject: Re: [PATCHv2.1 08/29] x86/tdx: Handle in-kernel MMIO

On Tue, Jan 25, 2022 at 02:04:32AM +0300, Kirill A. Shutemov wrote:
> MMIO addresses can be used with any CPU instruction that accesses
> memory. This patch, however, covers only MMIO accesses done via io.h

Just like the last time:

s/This patch, however, covers only/Address only/

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

> helpers, such as 'readl()' or 'writeq()'.
> 
> readX()/writeX() helpers limit the range of instructions which can trigger
> MMIO. It makes MMIO instruction emulation feasible. Raw access to MMIO

"Raw access to a MMIO region allows the compiler to ..."

> region allows compiler to generate whatever instruction it wants.
> Supporting all possible instructions is a task of a different scope
								     ^
								     . Fullstop


...

> @@ -149,6 +151,111 @@ static bool tdx_handle_cpuid(struct pt_regs *regs)
>  	return true;
>  }
>  
> +static int tdx_mmio(int size, bool write, unsigned long addr,
> +		     unsigned long *val)

You don't need to break that line.

Rest LGTM.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette