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

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Message-ID: <p34d7e5r3gkcj2xl5jycyldvpkmcllmhzioaqcmseeugl3eq73@plk43dd4luzu>
Date: Wed, 21 Feb 2024 16:15:27 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Baoquan He <bhe@...hat.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 Wed, Feb 21, 2024 at 10:37:29AM +0800, Baoquan He wrote:
> > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> > index 3612e3167147..425ff6e192e6 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -657,7 +657,8 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
> >  
> >  /*
> >   * Lookup the page table entry for a virtual address in a specific pgd.
> > - * Return a pointer to the entry and the level of the mapping.
> > + * Return a pointer to the entry and the level of the mapping (or NULL if
> > + * the entry is none) and level of the entry.
>                        ^ this right parenthesis may need be moved to the end.
> 
> 
> =======
>  * Return a pointer to the entry and the level of the mapping (or NULL if
>  * the entry is none and level of the entry).
> =======

Emm.. I like my variant more. We return level regardless if the entry none
or not. I don't see a reason to repeat it twice.

> >   */
> >  pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
> >  			     unsigned int *level)
> > @@ -704,9 +705,8 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
> >   * Lookup the page table entry for a virtual address. Return a pointer
> >   * to the entry and the level of the mapping.
> >   *
> > - * Note: We return pud and pmd either when the entry is marked large
> > - * or when the present bit is not set. Otherwise we would return a
> > - * pointer to a nonexisting mapping.
> > + * Note: the function returns p4d, pud and pmd either when the entry is marked
>                                           ~~~
>                                            ^ s/and/or/

Fair enough.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov