From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Joey Gouly <joey.gouly@arm.com>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH 2/2] KVM: arm64: Move FGT value configuration to vCPU state
Date: Fri, 17 Mar 2023 16:48:26 +0000 [thread overview]
Message-ID: <87zg8bgw85.wl-maz@kernel.org> (raw)
In-Reply-To: <855e60de-56c0-4500-a8ce-d79ffb0ed19d@sirena.org.uk>
On Fri, 17 Mar 2023 13:49:44 +0000,
Mark Brown <broonie@kernel.org> wrote:
>
> On Fri, Mar 17, 2023 at 09:02:32AM +0000, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
>
> > > + vcpu->arch.hfgrtr_el2 = 0;
> > > + vcpu->arch.hfgwtr_el2 = 0;
>
> > Although this looks completely innocent, this actually have the effect
> > of trapping the SMPRI_EL1 and TPIDR2_EL0 registers, something that is
> > self documented in the current code, and that completely disappears
> > with this patch.
>
> > This needs documenting by enumerating the sysregs that get trapped.
>
> That's an awful lot of registers with the fine grained traps, and when
> extended to cover HFHxTR2 there's a bunch of RES0 bits intended for
> future traps. It feels a bit unmanagable. I'd have expected something
> more along the lines of "enable all traps other than...". The pattern
> seemed to be more to have an explicit initialiser for the bits that are
> set (eg, with CPACR_EL1) which was why I didn't put anything explicit.
"an awful lot of registers" is exactly 3 registers as of ARMv8.8/9.3
that have a disable-trapping-when-set pattern. Maybe more in 9.4 and
up, but if people can be bothered to write the tools/sysreg file, they
can also document what gets implicitly trapped.
This also outlines that ACCDATA_EL1 gets trapped while it wasn't
explicitly trapped before, and that we don't have a handler for it.
So we need an extensive documentation of what the 0 value covers, no
ifs no buts.
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
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:[~2023-03-17 16:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 16:08 [PATCH 0/2] KVM: arm64: Support for per-guest fine grained traps configuration Mark Brown
2023-03-06 16:08 ` [PATCH 1/2] arm64: Add feature detection for fine grained traps Mark Brown
2023-03-15 15:34 ` Catalin Marinas
2023-03-06 16:08 ` [PATCH 2/2] KVM: arm64: Move FGT value configuration to vCPU state Mark Brown
2023-03-17 9:02 ` Marc Zyngier
2023-03-17 13:49 ` Mark Brown
2023-03-17 14:06 ` Mark Brown
2023-03-17 16:48 ` Marc Zyngier [this message]
2023-03-17 18:02 ` 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=87zg8bgw85.wl-maz@kernel.org \
--to=maz@kernel.org \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=james.morse@arm.com \
--cc=joey.gouly@arm.com \
--cc=kvmarm@lists.linux.dev \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=oliver.upton@linux.dev \
--cc=suzuki.poulose@arm.com \
--cc=will@kernel.org \
--cc=yuzenghui@huawei.com \
/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).