linux-kernel - Re: [PATCH] x86/mm: fix lookup_address() to handle physical memory holes in direct mapping

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Date: Fri, 28 Jun 2024 16:36:20 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>,
 "ashish.kalra@....com" <ashish.kalra@....com>,
 "peterz@...radead.org" <peterz@...radead.org>,
 "mingo@...hat.com" <mingo@...hat.com>, "luto@...nel.org" <luto@...nel.org>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "bp@...en8.de" <bp@...en8.de>
Cc: "jgross@...e.com" <jgross@...e.com>, "x86@...nel.org" <x86@...nel.org>,
 "Rodel, Jorg" <jroedel@...e.de>, "mhklinux@...look.com"
 <mhklinux@...look.com>, "hpa@...or.com" <hpa@...or.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
 "peterx@...hat.com" <peterx@...hat.com>,
 "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH] x86/mm: fix lookup_address() to handle physical memory
 holes in direct mapping

On 6/28/24 16:33, Edgecombe, Rick P wrote:
> On Fri, 2024-06-28 at 16:22 -0500, Kalra, Ashish wrote:
>>>> @@ -717,7 +718,11 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd,
>>>> unsigned
>>>> long address,
>>>>         *nx |= pmd_flags(*pmd) & _PAGE_NX;
>>>>         *rw &= pmd_flags(*pmd) & _PAGE_RW;
>>>>  
>>>> -       return pte_offset_kernel(pmd, address);
>>>> +       pte = pte_offset_kernel(pmd, address);
>>>> +       if (pte_none(*pte))
>>>> +               return NULL;
>>>> +
>>>> +       return pte;
>>> The other levels check for pXX_none() before adjusting *level. Not sure what
>>> the
>>> effect would be, but I think it should be the same behavior for all.
>>
>> If we are returning NULL, why should adjusting *level matter.
> 
> Well, I think symmetry is enough of a reason, but actually it should be ok.
> 
> I was looking at this diff compared to my working tree, but this tip commit

Ditto for me.

Thanks,
Tom

> (which is about that scenario) makes it set *level before checking none for all
> of them:
> https://lore.kernel.org/lkml/171871930159.10875.16081839197437299007.tip-bot2@tip-bot2/
> 
> So sorry, nevermind.