KVM ARM Archive on lore.kernel.org
 help / color / Atom feed
From: Rob Herring <robh@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	Marc Zyngier <maz@kernel.org>,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v3 3/3] arm64: Add workaround for Arm Cortex-A77 erratum 1508412
Date: Fri, 31 Jul 2020 16:55:26 -0600
Message-ID: <CAL_JsqKhytox6+rbZBbkgs2=Zgh3ZtXeYyzjqSWF6Picn-c27A@mail.gmail.com> (raw)
In-Reply-To: <20200730082227.GA24095@willie-the-truck>

On Thu, Jul 30, 2020 at 2:22 AM Will Deacon <will@kernel.org> wrote:
>
> On Wed, Jul 29, 2020 at 05:38:00PM +0100, Catalin Marinas wrote:
> > On Fri, Jul 17, 2020 at 02:52:33PM -0600, Rob Herring wrote:
> > > diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> > > index ce3080834bfa..ce5b0d9b12bf 100644
> > > --- a/arch/arm64/include/asm/kvm_hyp.h
> > > +++ b/arch/arm64/include/asm/kvm_hyp.h
> > > @@ -46,6 +46,17 @@
> > >  #define read_sysreg_el2(r) read_sysreg_elx(r, _EL2, _EL1)
> > >  #define write_sysreg_el2(v,r)      write_sysreg_elx(v, r, _EL2, _EL1)
> > >
> > > +static inline u64 __hyp_text read_sysreg_par(void)
> > > +{
> > > +   u64 par;
> > > +   if (cpus_have_const_cap(ARM64_WORKAROUND_1508412))
> > > +           dmb(sy);
> > > +   par = read_sysreg(par_el1);
> > > +   if (cpus_have_const_cap(ARM64_WORKAROUND_1508412))
> > > +           dmb(sy);
> > > +   return par;
> > > +}
> >
> > Even if that's not always called on a critical path, I agree with Andrew
> > that we could use alternatives here for dmb(sy).
>
> Even then, I'm not sure how this helps if the CPU can speculatively branch
> to the PAR access without executing the DMB. Is that not possible on A77?

I'm told by the h/w folks speculation is not possible in this case.

Rob
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 20:52 [PATCH v3 0/3] Cortex-A77 erratum 1508412 workaround Rob Herring
2020-07-17 20:52 ` [PATCH v3 1/3] KVM: arm64: Print warning when cpu erratum can cause guests to deadlock Rob Herring
2020-07-17 20:52 ` [PATCH v3 2/3] arm64: Add part number for Arm Cortex-A77 Rob Herring
2020-07-17 20:52 ` [PATCH v3 3/3] arm64: Add workaround for Arm Cortex-A77 erratum 1508412 Rob Herring
2020-07-27 15:52   ` Andrew Scull
2020-07-29 16:38   ` Catalin Marinas
2020-07-30  8:22     ` Will Deacon
2020-07-31 22:55       ` Rob Herring [this message]
2020-08-03 15:03         ` Will Deacon
2020-07-31 23:21     ` Rob Herring

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='CAL_JsqKhytox6+rbZBbkgs2=Zgh3ZtXeYyzjqSWF6Picn-c27A@mail.gmail.com' \
    --to=robh@kernel.org \
    --cc=catalin.marinas@arm.com \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --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

KVM ARM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvmarm/0 kvmarm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvmarm kvmarm/ https://lore.kernel.org/kvmarm \
		kvmarm@lists.cs.columbia.edu
	public-inbox-index kvmarm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/edu.columbia.cs.lists.kvmarm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git