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Re: [RFC PATCH 06/10] arm64/sve: Disallow VL setting for individual threads by default
- From: Yao Qi <qiyaoltc at gmail dot com>
- To: Dave Martin <Dave dot Martin at arm dot com>
- Cc: linux-arm-kernel at lists dot infradead dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Marc Zyngier <Marc dot Zyngier at arm dot com>, Alan Hayward <alan dot hayward at arm dot com>, Christoffer Dall <christoffer dot dall at linaro dot org>, linux-arch at vger dot kernel dot org, libc-alpha at sourceware dot org, Florian Weimer <fweimer at redhat dot com>, Joseph Myers <joseph at codesourcery dot com>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Torvald Riegel <triegel at redhat dot com>, gdb at sourceware dot org
- Date: Mon, 16 Jan 2017 11:34:39 +0000
- Subject: Re: [RFC PATCH 06/10] arm64/sve: Disallow VL setting for individual threads by default
- Authentication-results: sourceware.org; auth=none
- References: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com> <1484220369-23970-7-git-send-email-Dave.Martin@arm.com>
On 17-01-12 11:26:05, Dave Martin wrote:
> General-purpose code in userspace is not expected to work correctly
> if multiple threads are allowed to run concurrently with different
> vector lengths in a single process.
>
> This patch adds an explicit flag PR_SVE_SET_VL_THREAD to request
> this behaviour. Without the flag, vector length setting is
> permitted only for a single-threaded process (which matches the
> expected usage model of setting the vector length at process
> startup).
Hi Dave,
PR_SVE_SET_VL_THREAD can be arch-independent, IMO, because prctl
needs a scope. Looks some of them are system-wide, some of them are
about threads within the same process (like, PR_MPX_ENABLE_MANAGEMENT).
IOW, PR_SVE_SET_VL_THREAD can be general flag, to indicate the scope
of each new ptrcl command is per-thread.
I happen to see PR_SET_FP_MODE in man pages, which is about setting
FP register modes in runtime. It is a little similar to setting VL in
this patch. However the doc doesn't mention the effect or the scope
of this command.
--
Yao (齐尧)