From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
dave.martin@arm.com, daniel.kiss@arm.com,
Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
ascull@google.com, qperret@google.com, kernel-team@android.com
Subject: Re: [PATCH v2 05/11] arm64: sve: Provide a conditional update accessor for ZCR_ELx
Date: Fri, 19 Mar 2021 16:51:46 +0000 [thread overview]
Message-ID: <45a7868d83eaaef2e5d0f6e730c9c8f2@kernel.org> (raw)
In-Reply-To: <20210319164236.GH5619@sirena.org.uk>
On 2021-03-19 16:42, Mark Brown wrote:
> On Thu, Mar 18, 2021 at 12:25:26PM +0000, Marc Zyngier wrote:
>
>> A common pattern is to conditionally update ZCR_ELx in order
>> to avoid the "self-synchronizing" effect that writing to this
>> register has.
>>
>> Let's provide an accessor that does exactly this.
>
> Reviewed-by: Mark Brown <broonie@kernel.org>
>
>> +#define sve_cond_update_zcr_vq(val, reg) \
>> + do { \
>> + u64 __zcr = read_sysreg_s((reg)); \
>> + u64 __new = __zcr & ~ZCR_ELx_LEN_MASK; \
>> + __new |= (val) & ZCR_ELx_LEN_MASK; \
>> + if (__zcr != __new) \
>> + write_sysreg_s(__new, (reg)); \
>> + } while (0)
>> +
>
> Do compilers actually do much better with this than with a static
> inline like the other functions in this header? Seems like something
> they should be figuring out.
It's not about performance or anything of the sort: in most cases
where we end-up using this, it is on the back of an exception.
So performance is the least of our worries.
However, the "reg" parameter to read/write_sysreg_s() cannot
be a variable, because it is directly fed to the assembler.
If you want to use functions, you need to specialise them per
register. At this point, I'm pretty happy with a #define.
M.
--
Jazz is not dead. It just smells funny...
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-03-19 16:53 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 12:25 [PATCH v2 00/11] KVM: arm64: Enable SVE support on nVHE systems Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 01/11] KVM: arm64: Provide KVM's own save/restore SVE primitives Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 02/11] KVM: arm64: Use {read, write}_sysreg_el1 to access ZCR_EL1 Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 03/11] KVM: arm64: Let vcpu_sve_pffr() handle HYP VAs Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 04/11] KVM: arm64: Introduce vcpu_sve_vq() helper Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 05/11] arm64: sve: Provide a conditional update accessor for ZCR_ELx Marc Zyngier
2021-03-18 13:32 ` Will Deacon
2021-03-19 16:42 ` Mark Brown
2021-03-19 16:51 ` Marc Zyngier [this message]
2021-03-19 16:58 ` Mark Brown
2021-03-18 12:25 ` [PATCH v2 06/11] KVM: arm64: Rework SVE host-save/guest-restore Marc Zyngier
2021-03-18 13:34 ` Will Deacon
2021-03-18 12:25 ` [PATCH v2 07/11] KVM: arm64: Map SVE context at EL2 when available Marc Zyngier
2021-03-18 13:35 ` Will Deacon
2021-03-18 12:25 ` [PATCH v2 08/11] KVM: arm64: Save guest's ZCR_EL1 before saving the FPSIMD state Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 09/11] KVM: arm64: Trap host SVE accesses when the FPSIMD state is dirty Marc Zyngier
2021-03-18 14:11 ` Will Deacon
2021-03-18 14:29 ` Marc Zyngier
2021-03-18 18:40 ` Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 10/11] KVM: arm64: Save/restore SVE state for nVHE Marc Zyngier
2021-03-18 14:13 ` Will Deacon
2021-03-18 14:32 ` Marc Zyngier
2021-03-18 12:25 ` [PATCH v2 11/11] KVM: arm64: Enable SVE support " Marc Zyngier
2021-03-19 17:53 ` [PATCH v2 00/11] KVM: arm64: Enable SVE support on nVHE systems Mark Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=45a7868d83eaaef2e5d0f6e730c9c8f2@kernel.org \
--to=maz@kernel.org \
--cc=ascull@google.com \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=daniel.kiss@arm.com \
--cc=dave.martin@arm.com \
--cc=james.morse@arm.com \
--cc=julien.thierry.kdev@gmail.com \
--cc=kernel-team@android.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=qperret@google.com \
--cc=suzuki.poulose@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).