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

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Date: Thu, 22 Feb 2024 23:37:59 +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 02/22/24 at 04:04pm, Kirill A. Shutemov wrote:
> On Thu, Feb 22, 2024 at 07:01:41PM +0800, Baoquan He wrote:
> > On 02/21/24 at 04:15pm, Kirill A. Shutemov wrote:
> > > 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.
> > 
> > 
> >  * 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 (or NULL if
> >  * the entry is none) and level of the entry.
> > 
> > Hmm, I am confused. Why do we need to stress the level of the mapping
> > and level of the entry? Wondering what is the difference. I must miss
> > something.
> 
> My bad. This is way I meant to write:
> 
>  * Lookup the page table entry for a virtual address in a specific pgd.
>  * Return a pointer to the entry (or NULL if the entry does not exist) and
>  * the level of the entry.

ACK. Thanks.