From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Charlie Jenkins <charlie@rivosinc.com>,
Arnd Bergmann <arnd@arndb.de>,
Richard Henderson <richard.henderson@linaro.org>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
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Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
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"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
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Nicholas Piggin <npiggin@gmail.com>,
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linux-kselftest@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH RFC v2 0/4] mm: Introduce MAP_BELOW_HINT
Date: Fri, 30 Aug 2024 16:18:40 +0100 [thread overview]
Message-ID: <e48d41f5-646c-413e-99e5-c935b5235576@lucifer.local> (raw)
In-Reply-To: <a922737b-be1a-4ae9-b2d8-fefc44bb6419@intel.com>
On Fri, Aug 30, 2024 at 08:03:25AM GMT, Dave Hansen wrote:
> On 8/29/24 01:42, Lorenzo Stoakes wrote:
> >> These applications work on x86 because x86 does an implicit 47-bit
> >> restriction of mmap() address that contain a hint address that is less
> >> than 48 bits.
> > You mean x86 _has_ to limit to physically available bits in a canonical
> > format 🙂 this will not be the case for 5-page table levels though...
>
> By "physically available bits" are you referring to the bits that can be
> used as a part of the virtual address? "Physically" may not have been
> the best choice of words. ;)
>
> There's a canonical hole in 4-level paging and 5-level paging on x86.
> The 5-level canonical hole is just smaller.
Yeah sorry this is what I meant!
>
> Also, I should probably say that the >47-bit mmap() access hint was more
> of a crutch than something that we wanted to make ABI forever. We knew
> that high addresses might break some apps and we hoped that the list of
> things it would break would go down over time so that we could
> eventually just let mmap() access the whole address space by default.
>
> That optimism may have been misplaced.
Interesting, thanks. This speaks again I think to it being unwise to rely
on these things.
I do think the only workable form of this series is a fixed
personality-based mapping limit.
next prev parent reply other threads:[~2024-08-30 15:19 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-29 7:15 Charlie Jenkins
2024-08-29 7:15 ` [PATCH RFC v2 1/4] mm: Add MAP_BELOW_HINT Charlie Jenkins
2024-08-29 8:26 ` Michael Ellerman
2024-08-30 1:16 ` Charlie Jenkins
2024-08-29 7:15 ` [PATCH RFC v2 2/4] mm: Add hint and mmap_flags to struct vm_unmapped_area_info Charlie Jenkins
2024-08-29 8:48 ` Lorenzo Stoakes
2024-08-30 1:11 ` Charlie Jenkins
2024-09-03 17:18 ` Christophe Leroy
2024-08-29 7:16 ` [PATCH RFC v2 3/4] mm: Support MAP_BELOW_HINT in vm_unmapped_area() Charlie Jenkins
2024-08-29 7:16 ` [PATCH RFC v2 4/4] selftests/mm: Create MAP_BELOW_HINT test Charlie Jenkins
2024-08-29 8:30 ` [PATCH RFC v2 0/4] mm: Introduce MAP_BELOW_HINT Michal Hocko
2024-08-29 17:33 ` Charlie Jenkins
2024-09-03 8:44 ` Michal Hocko
2024-08-29 8:42 ` Lorenzo Stoakes
2024-08-29 9:54 ` Lorenzo Stoakes
2024-08-29 22:16 ` Charlie Jenkins
2024-08-30 9:52 ` Lorenzo Stoakes
2024-08-31 1:45 ` Charlie Jenkins
2024-08-30 15:03 ` Dave Hansen
2024-08-30 15:18 ` Lorenzo Stoakes [this message]
2024-08-29 9:02 ` Vlastimil Babka
2024-08-29 17:00 ` Palmer Dabbelt
2024-09-05 6:47 ` Kirill A. Shutemov
2024-09-05 17:26 ` Charlie Jenkins
2024-09-09 9:46 ` Kirill A. Shutemov
2024-10-21 13:22 ` Steven Price
2024-10-21 19:48 ` Liam R. Howlett
2024-10-23 9:31 ` Steven Price
2024-10-23 18:10 ` Liam R. Howlett
2024-10-24 10:52 ` Steven Price
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