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From: Ingo Molnar <mingo@kernel.org>
To: Baoquan He <bhe@redhat.com>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, yanjun.zhu@linux.dev,
	x86@kernel.org
Subject: Re: [PATCH v2 6/7] x86/mm: remove p4d_leaf definition
Date: Mon, 31 Mar 2025 11:57:28 +0200	[thread overview]
Message-ID: <Z-pnCLaAp43kJVCM@gmail.com> (raw)
In-Reply-To: <20250331081327.256412-7-bhe@redhat.com>


* Baoquan He <bhe@redhat.com> wrote:

> There's no p4d huge page support yet, let's use the generic definition.
> 
> And also update the BUILD_BUG_ON() in pti_user_pagetable_walk_pmd()
> because p4d_leaf() returns boolean value.


> -#define p4d_leaf p4d_leaf
> -static inline bool p4d_leaf(p4d_t p4d)
> -{
> -	/* No 512 GiB pages yet */
> -	return 0;
> -}

This comment was also incorrect I believe:

1 PTE entry on x86-64 covers 4K virtual memory, 512 PTE entries make up 
a 4K pagetable page, and each level of paging adds another level of 512 
pagetable entries:

 - level 0:                 4K pages
 - level 1: 512x    4K =   2MB 'large' pages
 - level 2: 512x   2MB =   1GB 'huge' pages
 - level 3: 512x   1GB = 512GB 'PGD' pages
 - level 4: 512x 512GB = 256TB 'P4D' pages

So the above comment should have said '256 TB' pages, unless there's 
some naming weirdness I missed.

Thanks,

	Ingo

  reply	other threads:[~2025-03-31  9:57 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-03-31  8:13 [PATCH v2 0/7] mm/gup: Minor fix, cleanup and improvements Baoquan He
2025-03-31  8:13 ` [PATCH v2 1/7] mm/gup: fix wrongly calculated returned value in fault_in_safe_writeable() Baoquan He
2025-04-01  8:10   ` David Hildenbrand
2025-04-01 14:00     ` Oscar Salvador
2025-04-01 14:12       ` Baoquan He
2025-04-01 14:11     ` Baoquan He
2025-03-31  8:13 ` [PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier Baoquan He
2025-04-01  8:02   ` David Hildenbrand
2025-04-01 14:34     ` Baoquan He
2025-04-01 14:37       ` David Hildenbrand
2025-04-02  1:26         ` Baoquan He
2025-03-31  8:13 ` [PATCH v2 3/7] mm/gup: Fix the outdated code comments above get_user_pages_unlocked() Baoquan He
2025-04-01  8:14   ` David Hildenbrand
2025-04-01 14:36     ` Baoquan He
2025-04-01 13:51   ` Oscar Salvador
2025-04-01 15:29     ` Baoquan He
2025-03-31  8:13 ` [PATCH v2 4/7] mm/gup: remove gup_fast_pgd_leaf() and clean up the relevant codes Baoquan He
2025-04-01  8:19   ` David Hildenbrand
2025-04-01 14:11   ` Oscar Salvador
2025-03-31  8:13 ` [PATCH v2 5/7] x86/mm: remove pgd_leaf definition in arch Baoquan He
2025-03-31 10:25   ` [tip: x86/mm] x86/mm: Simplify the pgd_leaf() and p4d_leaf() checks a bit tip-bot2 for Baoquan He
2025-03-31 10:26   ` [tip: x86/mm] x86/mm: Remove the arch-specific pgd_leaf() definition tip-bot2 for Baoquan He
2025-04-01  8:21   ` [PATCH v2 5/7] x86/mm: remove pgd_leaf definition in arch David Hildenbrand
2025-04-01 14:03   ` Oscar Salvador
2025-04-02  3:39     ` Baoquan He
2025-04-01 20:53   ` [tip: x86/mm] x86/mm: Simplify the pgd_leaf() and p4d_leaf() checks a bit tip-bot2 for Baoquan He
2025-04-01 20:53   ` [tip: x86/mm] x86/mm: Remove the arch-specific pgd_leaf() definition tip-bot2 for Baoquan He
2025-04-01 21:03   ` [tip: x86/mm] x86/mm: Simplify the pgd_leaf() and p4d_leaf() checks a bit tip-bot2 for Baoquan He
2025-03-31  8:13 ` [PATCH v2 6/7] x86/mm: remove p4d_leaf definition Baoquan He
2025-03-31  9:57   ` Ingo Molnar [this message]
2025-03-31 14:20     ` Baoquan He
2025-04-01  7:20       ` Ingo Molnar
2025-04-03 13:44         ` Baoquan He
2025-03-31 10:25   ` [tip: x86/mm] x86/mm: Remove the arch-specific p4d_leaf() definition tip-bot2 for Baoquan He
2025-04-01 14:05   ` [PATCH v2 6/7] x86/mm: remove p4d_leaf definition Oscar Salvador
2025-04-01 20:53   ` [tip: x86/mm] x86/mm: Remove the arch-specific p4d_leaf() definition tip-bot2 for Baoquan He
2025-04-01 21:03   ` tip-bot2 for Baoquan He
2025-03-31  8:13 ` [PATCH v2 7/7] mm/pgtable: remove unneeded pgd_devmap() Baoquan He
2025-04-01  8:21   ` David Hildenbrand
2025-04-02  3:33     ` Baoquan He

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