linux-kernel - Re: [PATCH v6 6/8] x86/sev: Treat the contiguous RMP table as a single RMP segment

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Message-ID: <20241209194320.GCZ1dIWDMPppdXgzxJ@fat_crate.local>
Date: Mon, 9 Dec 2024 20:43:20 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Michael Roth <michael.roth@....com>,
	Ashish Kalra <ashish.kalra@....com>,
	Nikunj A Dadhania <nikunj@....com>,
	Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Subject: Re: [PATCH v6 6/8] x86/sev: Treat the contiguous RMP table as a
 single RMP segment

On Mon, Dec 02, 2024 at 02:50:51PM -0600, Tom Lendacky wrote:
>  static struct rmpentry_raw *get_raw_rmpentry(u64 pfn)
>  {
> -	if (!rmptable)
> +	u64 paddr, rst_index, segment_index;
> +	struct rmp_segment_desc *desc;
> +
> +	if (!rmp_segment_table)
>  		return ERR_PTR(-ENODEV);
>  
> -	if (unlikely(pfn > rmptable_max_pfn))
> +	paddr = pfn << PAGE_SHIFT;
> +
> +	rst_index = RST_ENTRY_INDEX(paddr);
> +	if (unlikely(rst_index >= rst_max_index))
> +		return ERR_PTR(-EFAULT);
> +	rst_index = array_index_nospec(rst_index, rst_max_index);

I think we should collect the deliberation why we're doing this nospec stuff
from here:

https://lore.kernel.org/r/79be2e29-6487-dd60-9b6f-3daa48a2e93f@amd.com

into a comment around here for future reference.

This is the best example for those: "uff, why did we do it back then"?
questions when we stare at this months, years from now.


-- 
Regards/Gruss,
    Boris.

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