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From: David Laight <David.Laight@ACULAB.COM>
To: 'Steven Price' <steven.price@arm.com>,
	Amanieu d'Antras <amanieu@gmail.com>
Cc: Arnd Bergmann <arnd@kernel.org>,
	Ryan Houdek <Houdek.Ryan@fex-emu.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Mark Brown <broonie@kernel.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: RE: [RESEND PATCH v4 8/8] arm64: Allow 64-bit tasks to invoke compat syscalls
Date: Mon, 24 May 2021 12:38:19 +0000	[thread overview]
Message-ID: <f0d09966f7714c54aee1bb0260a6193d@AcuMS.aculab.com> (raw)
In-Reply-To: <419f410f-21b3-a4c6-3cd8-025007e9c31e@arm.com>

From: Steven Price
> Sent: 24 May 2021 12:21
...
> So a "generic" way of requested the kernel limit the address space for
> allocations would be potentially useful for other purposes. Adding a new
> syscall for this purpose would be sensible. We already have (at least)
> two "hacks" in mmap for controlling the address range that can be used:
> 
>  * MAP_32BIT - x86 only, and really "31 bit"
> 
>  * Providing a mmap() hint with the top bits set to opt-in to 52-bit VAs.
> 
> A well defined mechanism for controlling the valid VA range for
> allocations would be much better than adding more hacks - and bonus
> points if it works for all the different types of allocation unlike the
> above.

I'd have thought a 'MAP_BELOW' flag (cf MAP_FIXED) would suffice.
I'm sort of surprised MAP_32BIT wasn't implemented that way.
'man mmap' says MAP_32BIT was added for x64 thread stacks - I though
the requirement can from 32bit wine (windows has a 2G user/kernel boundary).

	David

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  reply	other threads:[~2021-05-24 23:22 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-18  9:06 [RESEND PATCH v4 0/8] " Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 1/8] mm: Add arch_get_mmap_base_topdown macro Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 2/8] hugetlbfs: Use arch_get_mmap_* macros Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 3/8] mm: Support mmap_compat_base with the generic layout Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 4/8] arm64: Separate in_compat_syscall from is_compat_task Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 5/8] arm64: mm: Use HAVE_ARCH_COMPAT_MMAP_BASES Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 6/8] arm64: Add a compat syscall flag to thread_info Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 7/8] arm64: Forbid calling compat sigreturn from 64-bit tasks Amanieu d'Antras
2021-05-18  9:06 ` [RESEND PATCH v4 8/8] arm64: Allow 64-bit tasks to invoke compat syscalls Amanieu d'Antras
2021-05-18 13:02   ` Arnd Bergmann
2021-05-18 20:26     ` David Laight
2021-05-18 22:41       ` Ryan Houdek
2021-05-18 23:51     ` Amanieu d'Antras
2021-05-19 15:30       ` Steven Price
2021-05-19 16:14         ` Amanieu d'Antras
2021-05-21  8:51           ` Steven Price
2021-05-21 19:18             ` Amanieu d'Antras
2021-05-24 11:20               ` Steven Price
2021-05-24 12:38                 ` David Laight [this message]
2021-05-18 23:52     ` Ryan Houdek

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