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From: Alexandru Elisei <alexandru.elisei@arm.com>
To: drjones@redhat.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu
Subject: [kvm-unit-tests PATCH 1/6] arm64: Remove unnecessary ISB when writing to SPSel
Date: Sat, 27 Feb 2021 10:41:56 +0000	[thread overview]
Message-ID: <20210227104201.14403-2-alexandru.elisei@arm.com> (raw)
In-Reply-To: <20210227104201.14403-1-alexandru.elisei@arm.com>

Software can use the SPSel operand to write directly to PSTATE.SP.
According to ARM DDI 0487F.b, page D1-2332, writes to PSTATE are
self-synchronizing and no ISB is needed:

"Writes to the PSTATE fields have side-effects on various aspects of the PE
operation. All of these side-effects are guaranteed:
- Not to be visible to earlier instructions in the execution stream.
- To be visible to later instructions in the execution stream."

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arm/cstart64.S | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arm/cstart64.S b/arm/cstart64.S
index 0428014aa58a..fc1930bcdb53 100644
--- a/arm/cstart64.S
+++ b/arm/cstart64.S
@@ -54,7 +54,6 @@ start:
 	/* set up stack */
 	mov	x4, #1
 	msr	spsel, x4
-	isb
 	adrp    x4, stackptr
 	add     sp, x4, :lo12:stackptr
 
-- 
2.30.1


WARNING: multiple messages have this Message-ID (diff)
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: drjones@redhat.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu
Subject: [kvm-unit-tests PATCH 1/6] arm64: Remove unnecessary ISB when writing to SPSel
Date: Sat, 27 Feb 2021 10:41:56 +0000	[thread overview]
Message-ID: <20210227104201.14403-2-alexandru.elisei@arm.com> (raw)
In-Reply-To: <20210227104201.14403-1-alexandru.elisei@arm.com>

Software can use the SPSel operand to write directly to PSTATE.SP.
According to ARM DDI 0487F.b, page D1-2332, writes to PSTATE are
self-synchronizing and no ISB is needed:

"Writes to the PSTATE fields have side-effects on various aspects of the PE
operation. All of these side-effects are guaranteed:
- Not to be visible to earlier instructions in the execution stream.
- To be visible to later instructions in the execution stream."

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arm/cstart64.S | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arm/cstart64.S b/arm/cstart64.S
index 0428014aa58a..fc1930bcdb53 100644
--- a/arm/cstart64.S
+++ b/arm/cstart64.S
@@ -54,7 +54,6 @@ start:
 	/* set up stack */
 	mov	x4, #1
 	msr	spsel, x4
-	isb
 	adrp    x4, stackptr
 	add     sp, x4, :lo12:stackptr
 
-- 
2.30.1

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  reply	other threads:[~2021-02-27 10:42 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-27 10:41 [kvm-unit-tests PATCH 0/6] Misc assembly fixes and cleanups Alexandru Elisei
2021-02-27 10:41 ` Alexandru Elisei
2021-02-27 10:41 ` Alexandru Elisei [this message]
2021-02-27 10:41   ` [kvm-unit-tests PATCH 1/6] arm64: Remove unnecessary ISB when writing to SPSel Alexandru Elisei
2021-03-03 17:35   ` Andre Przywara
2021-03-03 17:35     ` Andre Przywara
2021-02-27 10:41 ` [kvm-unit-tests PATCH 2/6] arm/arm64: Remove dcache_line_size global variable Alexandru Elisei
2021-02-27 10:41   ` Alexandru Elisei
2021-03-04 15:00   ` Andre Przywara
2021-03-04 15:00     ` Andre Przywara
2021-03-15 15:46     ` Alexandru Elisei
2021-03-15 15:46       ` Alexandru Elisei
2021-03-16 15:40       ` Andre Przywara
2021-03-16 15:40         ` Andre Przywara
2021-03-22 12:01         ` Alexandru Elisei
2021-03-22 12:01           ` Alexandru Elisei
2021-02-27 10:41 ` [kvm-unit-tests PATCH 3/6] arm/arm64: Remove unnecessary ISB when doing dcache maintenance Alexandru Elisei
2021-02-27 10:41   ` Alexandru Elisei
2021-03-12 14:59   ` Andrew Jones
2021-03-12 14:59     ` Andrew Jones
2021-03-15 16:22     ` Alexandru Elisei
2021-03-15 16:22       ` Alexandru Elisei
2021-02-27 10:41 ` [kvm-unit-tests PATCH 4/6] lib: arm64: Consolidate register definitions to sysreg.h Alexandru Elisei
2021-02-27 10:41   ` Alexandru Elisei
2021-03-03 17:32   ` Andre Przywara
2021-03-03 17:32     ` Andre Przywara
2021-02-27 10:42 ` [kvm-unit-tests PATCH 5/6] arm64: Configure SCTLR_EL1 at boot Alexandru Elisei
2021-02-27 10:42   ` Alexandru Elisei
2021-03-03 17:32   ` Andre Przywara
2021-03-03 17:32     ` Andre Przywara
2021-02-27 10:42 ` [kvm-unit-tests PATCH 6/6] arm64: Disable TTBR1_EL1 translation table walks Alexandru Elisei
2021-02-27 10:42   ` Alexandru Elisei
2021-03-03 17:32   ` Andre Przywara
2021-03-03 17:32     ` Andre Przywara

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