linux-kernel - Re: [PATCH v5 19/25] arm64/mm: Wire up PTE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <39ee7f6b-082e-4bab-98e1-dc2130131160@redhat.com>
Date: Tue, 13 Feb 2024 11:01:09 +0100
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>, Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>,
 James Morse <james.morse@....com>, Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, John Hubbard
 <jhubbard@...dia.com>, Zi Yan <ziy@...dia.com>,
 Barry Song <21cnbao@...il.com>, Alistair Popple <apopple@...dia.com>,
 Yang Shi <shy828301@...il.com>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, linux-arm-kernel@...ts.infradead.org,
 x86@...nel.org, linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 19/25] arm64/mm: Wire up PTE_CONT for user mappings

On 12.02.24 21:38, Ryan Roberts wrote:
> [...]
> 
>>>>> +static inline bool mm_is_user(struct mm_struct *mm)
>>>>> +{
>>>>> +	/*
>>>>> +	 * Don't attempt to apply the contig bit to kernel mappings, because
>>>>> +	 * dynamically adding/removing the contig bit can cause page faults.
>>>>> +	 * These racing faults are ok for user space, since they get serialized
>>>>> +	 * on the PTL. But kernel mappings can't tolerate faults.
>>>>> +	 */
>>>>> +	return mm != &init_mm;
>>>>> +}
>>>>
>>>> We also have the efi_mm as a non-user mm, though I don't think we manipulate
>>>> that while it is live, and I'm not sure if that needs any special handling.
>>>
>>> Well we never need this function in the hot (order-0 folio) path, so I think I
>>> could add a check for efi_mm here with performance implication. It's probably
>>> safest to explicitly exclude it? What do you think?
>>
>> Oops: This should have read "I think I could add a check for efi_mm here
>> *without* performance implication"
> 
> It turns out that efi_mm is only defined when CONFIG_EFI is enabled. I can do this:
> 
> return mm != &init_mm && (!IS_ENABLED(CONFIG_EFI) || mm != &efi_mm);

Please use all the lines you need ;)

if (IS_ENABLED(CONFIG_EFI) && unlikely(mm == &efi_mm))
	return false;
return mm != &init_mm;

> 
> Is that acceptable? This is my preference, but nothing else outside of efi
> references this symbol currently.

We could also mark MMs in some way to be special.

return mm->is_user;

Then it's easy to extend.

-- 
Cheers,

David / dhildenb