From: Andre Przywara <andre.przywara@arm.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: drjones@redhat.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu
Subject: Re: [kvm-unit-tests PATCH 1/6] arm64: Remove unnecessary ISB when writing to SPSel
Date: Wed, 3 Mar 2021 17:35:57 +0000 [thread overview]
Message-ID: <20210303173557.0626667d@slackpad.fritz.box> (raw)
In-Reply-To: <20210227104201.14403-2-alexandru.elisei@arm.com>
On Sat, 27 Feb 2021 10:41:56 +0000
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 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>
I am always a bit wary about *removing* barriers, but I can confirm
that the ARM ARM indeed makes this guarantee above, and SP access
sounds like an easy enough case, so:
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Cheers,
Andre
> ---
> 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
>
next prev parent reply other threads:[~2021-03-04 0:30 UTC|newest]
Thread overview: 17+ 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 ` [kvm-unit-tests PATCH 1/6] arm64: Remove unnecessary ISB when writing to SPSel Alexandru Elisei
2021-03-03 17:35 ` Andre Przywara [this message]
2021-02-27 10:41 ` [kvm-unit-tests PATCH 2/6] arm/arm64: Remove dcache_line_size global variable Alexandru Elisei
2021-03-04 15:00 ` Andre Przywara
2021-03-15 15:46 ` Alexandru Elisei
2021-03-16 15:40 ` Andre Przywara
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
2021-03-12 14:59 ` Andrew Jones
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
2021-03-03 17:32 ` Andre Przywara
2021-02-27 10:42 ` [kvm-unit-tests PATCH 5/6] arm64: Configure SCTLR_EL1 at boot Alexandru Elisei
2021-03-03 17:32 ` Andre Przywara
2021-02-27 10:42 ` [kvm-unit-tests PATCH 6/6] arm64: Disable TTBR1_EL1 translation table walks Alexandru Elisei
2021-03-03 17:32 ` Andre Przywara
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