linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
From: Sudeep Holla <sudeep.holla@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v1 2/2] arm64: smccc: Support SMCCC v1.3 SVE register saving hint
Date: Tue, 18 May 2021 17:43:02 +0100	[thread overview]
Message-ID: <20210518164302.ldogm56xvhccnyas@bogus> (raw)
In-Reply-To: <20210518100919.6674-3-broonie@kernel.org>

Hi Mark,

On Tue, May 18, 2021 at 11:09:19AM +0100, Mark Brown wrote:
> SMCCC v1.2 requires that all SVE state be preserved over SMC calls which
> introduces substantial overhead in the common case where there is no SVE
> state in the registers. To avoid this SMCCC v1.3 introduces a flag which
> allows the caller to say that there is no state that needs to be preserved
> in the registers. Make use of this flag, setting it if the SMCCC version
> indicates support for it and the TIF_ flags indicate that there is no live
> SVE state in the registers, this avoids placing any constraints on when
> SMCCC calls can be done or triggering extra saving and reloading of SVE
> register state in the kernel.
> 
> This would be straightforward enough except for the rather entertaining
> inline assembly we use to do SMCCC v1.1 calls to allow us to take advantage
> of the limited number of registers it clobbers. Deal with this by having a
> slightly non-standard function which we call immediately before issuing the
> SMCCC call to make our checks. This causes an extra function call on any
> system built with SVE support, and extra checks when SVE is detected at
> runtime, but these costs are expected to be reasonable in the context of
> doing a SMCCC call in the first place.
> 

I am adding another interface that extends the input/output register set
for v1.2 and above. I assume we may need these changes there too. I have
cc-ed you in the updated version I just posted. The lore link is not yet
available, so sharing the one for earlier version[1]

-- 
Regards,
Sudeep

[1] https://lore.kernel.org/r/20210505093843.3308691-2-sudeep.holla@arm.com/

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-05-18 16:45 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-18 10:09 [PATCH v1 0/2] arm64: Implement SMCCC v1.3 SVE register saving hint Mark Brown
2021-05-18 10:09 ` [PATCH v1 1/2] arm64: asmlinkage: Enable use of BTI_C macro in SYM_CODE Mark Brown
2021-05-18 10:09 ` [PATCH v1 2/2] arm64: smccc: Support SMCCC v1.3 SVE register saving hint Mark Brown
2021-05-18 10:53   ` Marc Zyngier
2021-05-18 11:53     ` Mark Brown
2021-05-18 12:14       ` Marc Zyngier
2021-05-18 13:01         ` Mark Brown
2021-05-18 16:53     ` Ard Biesheuvel
2021-05-18 16:43   ` Sudeep Holla [this message]
2021-05-18 16:55     ` 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=20210518164302.ldogm56xvhccnyas@bogus \
    --to=sudeep.holla@arm.com \
    --cc=broonie@kernel.org \
    --cc=catalin.marinas@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=lorenzo.pieralisi@arm.com \
    --cc=mark.rutland@arm.com \
    --cc=maz@kernel.org \
    --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).