linux-kernel - Re: [PATCHv7 07/16] x86/mm: Return correct level from lookup

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Date: Mon, 19 Feb 2024 13:12:32 +0800
From: Baoquan He <bhe@...hat.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	"Kalra, Ashish" <ashish.kalra@....com>,
	Sean Christopherson <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>, kexec@...ts.infradead.org,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 07/16] x86/mm: Return correct level from
 lookup_address() if pte is none

On 02/12/24 at 12:44pm, Kirill A. Shutemov wrote:
> lookup_address() only returns correct page table level for the entry if
> the entry is not none.
> 
> Make the helper to always return correct 'level'. It allows to implement
> iterator over kernel page tables using lookup_address().
> 
> Add one more entry into enum pg_level to indicate size of VA covered by
> one PGD entry in 5-level paging mode.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
>  arch/x86/include/asm/pgtable_types.h | 1 +
>  arch/x86/mm/pat/set_memory.c         | 8 ++++----
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 0b748ee16b3d..3f648ffdfbe5 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -548,6 +548,7 @@ enum pg_level {
>  	PG_LEVEL_2M,
>  	PG_LEVEL_1G,
>  	PG_LEVEL_512G,
> +	PG_LEVEL_256T,
>  	PG_LEVEL_NUM
>  };
>  
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index f92da8c9a86d..3612e3167147 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -666,32 +666,32 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,

LGTM,

Reviewed-by: Baoquan He <bhe@...hat.com>

By the way, we may need update the code comment above function
lookup_address_in_pgd() and function lookup_address() since they don't
reflect the latest behaviour of them.

>  	pud_t *pud;
>  	pmd_t *pmd;
>  
> -	*level = PG_LEVEL_NONE;
> +	*level = PG_LEVEL_256T;
>  
>  	if (pgd_none(*pgd))
>  		return NULL;
>  
> +	*level = PG_LEVEL_512G;
>  	p4d = p4d_offset(pgd, address);
>  	if (p4d_none(*p4d))
>  		return NULL;
>  
> -	*level = PG_LEVEL_512G;
>  	if (p4d_large(*p4d) || !p4d_present(*p4d))
>  		return (pte_t *)p4d;
>  
> +	*level = PG_LEVEL_1G;
>  	pud = pud_offset(p4d, address);
>  	if (pud_none(*pud))
>  		return NULL;
>  
> -	*level = PG_LEVEL_1G;
>  	if (pud_large(*pud) || !pud_present(*pud))
>  		return (pte_t *)pud;
>  
> +	*level = PG_LEVEL_2M;
>  	pmd = pmd_offset(pud, address);
>  	if (pmd_none(*pmd))
>  		return NULL;
>  
> -	*level = PG_LEVEL_2M;
>  	if (pmd_large(*pmd) || !pmd_present(*pmd))
>  		return (pte_t *)pmd;
>  
> -- 
> 2.43.0
>