Messages in this thread | | | Subject | Re: [PATCH] x86/mm: Make pud_present() check _PAGE_PROTNONE and _PAGE_PSE as well | From | Anshuman Khandual <> | Date | Fri, 20 Mar 2020 18:52:57 +0530 |
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On 03/20/2020 05:17 PM, Kirill A. Shutemov wrote: > On Fri, Mar 20, 2020 at 08:53:16AM +0530, Anshuman Khandual wrote: >> >> >> On 03/18/2020 10:31 AM, Anshuman Khandual wrote: >>> pud_present() should also check _PAGE_PROTNONE and _PAGE_PSE bits like in >>> case pmd_present(). This makes a PUD entry test positive for pud_present() >>> after getting invalidated with pud_mknotpresent(), hence standardizing the >>> semantics with PMD helpers. >>> >>> Cc: Thomas Gleixner <tglx@linutronix.de> >>> Cc: Ingo Molnar <mingo@redhat.com> >>> Cc: Borislav Petkov <bp@alien8.de> >>> Cc: "H. Peter Anvin" <hpa@zytor.com> >>> Cc: Dave Hansen <dave.hansen@intel.com> >>> Cc: Andrew Morton <akpm@linux-foundation.org> >>> Cc: x86@kernel.org >>> Cc: linux-mm@kvack.org >>> Cc: linux-kernel@vger.kernel.org >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >>> --- >>> Even though pud_mknotpresent() is not used any where currently, there is >>> a discrepancy between PMD and PUD. >>> >>> WARN_ON(!pud_present(pud_mknotpresent(pud_mkhuge(pud)))) -> Fail >>> WARN_ON(!pmd_present(pmd_mknotpresent(pmd_mkhuge(pmd)))) -> Pass >>> >>> Though pud_mknotpresent() currently clears _PAGE_PROTNONE, pud_present() >>> does not check it. This change fixes both inconsistencies. >>> >>> This has been build and boot tested on x86. >> >> Adding Kirill and Dan. >> >> +Cc: Kirill A. Shutemov <kirill@shutemov.name> >> +Cc: Dan Williams <dan.j.williams@intel.com> > > Or we can just drop the pud_mknotpresent(). There's no users AFAICS and > only x86 provides it.
Yes that will be an option but IMHO fixing pud_present() here might be a better choice because,
(1) pud_mknotpresent() with fixed pud_present() might be required later (2) PMD & PUD will be exact same (THP is supported on either level)
Nonetheless, I am happy to go either way.
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