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@xxxxxxxxxxxxx> >>> Cc: Ingo Molnar <mingo@xxxxxxxxxx> >>> Cc: Borislav Petkov <bp@xxxxxxxxx> >>> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> >>> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> >>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>> Cc: x86@xxxxxxxxxx >>> Cc: linux-mm@xxxxxxxxx >>> Cc: linux-kernel@xxxxxxxxxxxxxxx >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> >>> --- >>> 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@xxxxxxxxxxxxx> >> +Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > 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.
