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[RFC PATCH 10/10] Revert "arm64/sve: Limit vector length to 512 bits by default"
- From: Dave Martin <Dave dot Martin at arm dot com>
- To: linux-arm-kernel at lists dot infradead dot org
- Cc: 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, Yao Qi <qiyaoltc at gmail dot com>
- Date: Thu, 12 Jan 2017 11:26:09 +0000
- Subject: [RFC PATCH 10/10] Revert "arm64/sve: Limit vector length to 512 bits by default"
- Authentication-results: sourceware.org; auth=none
- References: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com>
This reverts commit cdedb254ccddd9c6a8db91b3737690327e48dfe7.
Vector length limiting via Kconfig is no longer required now that
the default vector length can be manipulated at runtime via procfs.
---
arch/arm64/Kconfig | 35 -----------------------------------
arch/arm64/mm/proc.S | 5 -----
2 files changed, 40 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 98c0934..bced568 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -900,41 +900,6 @@ config ARM64_SVE
To enable use of this extension on CPUs that implement it, say Y.
-if ARM64_SVE
-
-config ARM64_SVE_FULL_VECTOR_LENGTH
- bool "Enable full hardware vector length for userspace"
- default n
- help
- SVE vector lengths greater than 512 bits impact the size of signal
- frames and therefore the size requirements for any userspace stack
- onto which a signal may be delivered. Using larger vector lengths
- may therefore cause problems for some software. For this reason, the
- kernel currently limits the maximum vector length for userspace
- software to 512 bits by default.
-
- Enabling this option removes the limit, so that the full vector
- length implemented by the hardware is made available to userspace.
-
- Be aware: in general, software that (a) does not use SVE (including
- via libraries), or (b) does not handle signals, or (c) uses default
- process/thread stack sizes and does not use sigaltstack(2) should be
- unaffected by enabling larger vectors. Software that does not meet
- these criteria or that relies on certain legacy uses of the ucontext
- API may be affected however.
-
- This is a transitional compatibility option only and will be replaced
- by a userspace ABI extension in the future. Do not assume that this
- option will be available with compatible effect in future Linux
- releases.
-
- If you are developing software that uses SVE and understand the
- implications, you can consider saying Y here.
-
- If unsure, say N.
-
-endif
-
config ARM64_MODULE_CMODEL_LARGE
bool
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index da2d602..aa96b4c 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -200,11 +200,6 @@ ENTRY(__cpu_setup)
mrs_s x5, ZIDR_EL1 // SVE: Enable full vector len
and x5, x5, #ZCR_EL1_LEN_MASK // initially
-#ifndef CONFIG_ARM64_SVE_FULL_VECTOR_LENGTH
- mov x6, #(512 / 128 - 1) // Clamp VL to 512 bits
- cmp x5, x6
- csel x5, x5, x6, lo
-#endif
msr_s ZCR_EL1, x5
b 2f
--
2.1.4