linux-kernel - Re: [PATCH] x86/mm: fix lookup_address() to handle physical memory holes in direct mapping

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Date: Fri, 28 Jun 2024 20:58:24 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "tglx@...utronix.de" <tglx@...utronix.de>, "Ashish.Kalra@....com"
	<Ashish.Kalra@....com>, "peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>, "luto@...nel.org" <luto@...nel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "bp@...en8.de"
	<bp@...en8.de>
CC: "jgross@...e.com" <jgross@...e.com>, "x86@...nel.org" <x86@...nel.org>,
	"mhklinux@...look.com" <mhklinux@...look.com>, "Rodel, Jorg"
	<jroedel@...e.de>, "hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"peterx@...hat.com" <peterx@...hat.com>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>
Subject: Re: [PATCH] x86/mm: fix lookup_address() to handle physical memory
 holes in direct mapping

On Fri, 2024-06-28 at 20:52 +0000, Ashish Kalra wrote:
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 443a97e515c0..be8b5bf3bc3f 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -672,6 +672,7 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd, unsigned
> long address,
>         p4d_t *p4d;
>         pud_t *pud;
>         pmd_t *pmd;
> +       pte_t *pte;
>  
>         *level = PG_LEVEL_256T;
>         *nx = false;
> @@ -717,7 +718,11 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd, unsigned
> long address,
>         *nx |= pmd_flags(*pmd) & _PAGE_NX;
>         *rw &= pmd_flags(*pmd) & _PAGE_RW;
>  
> -       return pte_offset_kernel(pmd, address);
> +       pte = pte_offset_kernel(pmd, address);
> +       if (pte_none(*pte))
> +               return NULL;
> +
> +       return pte;

The other levels check for pXX_none() before adjusting *level. Not sure what the
effect would be, but I think it should be the same behavior for all.