From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 3/5] arm64: kernel: Add min/max values in feature-detection register values.
Date: Fri, 17 Jul 2015 11:51:11 +0100 [thread overview]
Message-ID: <20150717105110.GL18994@arm.com> (raw)
In-Reply-To: <1437062519-18883-4-git-send-email-james.morse@arm.com>
On Thu, Jul 16, 2015 at 05:01:57PM +0100, James Morse wrote:
> When a new cpu feature is available, the cpu feature bits will be 0001,
> when features are updated, this value will be incremented. This patch
> changes 'register_value' to be '{min,max}_register_value', and checks
> the value falls in this range.
I'm not sure this is completely true. For example, the new atomics are
advertised with feature bits of 0002, whilst 0001 is RESERVED and 0000
means they're not present.
Also, the problem with specifying an upper bound is that we have to keep
updating it. Elsewhere in the kernel, we've treated these as 4-bit signed
fields and if X > Y, we assume that the feature set of X is a superset of
Y. Unfortunately, the ARM ARM doesn't provide this insight but it is
something that we teased out of the architects.
Does PAN break our assumptions here?
Will
next prev parent reply other threads:[~2015-07-17 10:51 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-16 16:01 [PATCH 0/5] arm64: kernel: Add support for Privileged Access Never James Morse
2015-07-16 16:01 ` [PATCH 1/5] arm64: kernel: preparatory: Move config_sctlr_el1 James Morse
2015-07-17 11:06 ` Catalin Marinas
2015-07-17 12:59 ` Catalin Marinas
2015-07-16 16:01 ` [PATCH 2/5] arm64: kernel: Add cpufeature 'enable' callback James Morse
2015-07-17 11:06 ` Catalin Marinas
2015-07-16 16:01 ` [PATCH 3/5] arm64: kernel: Add min/max values in feature-detection register values James Morse
2015-07-17 10:51 ` Will Deacon [this message]
2015-07-17 11:05 ` Catalin Marinas
2015-07-17 11:05 ` James Morse
2015-07-17 12:45 ` Will Deacon
2015-07-16 16:01 ` [PATCH 4/5] arm64: kernel: Add optional CONFIG_ parameter to ALTERNATIVE() James Morse
2015-07-17 11:08 ` Catalin Marinas
2015-07-16 16:01 ` [PATCH 5/5] arm64: kernel: Add support for Privileged Access Never James Morse
2015-07-17 12:57 ` Catalin Marinas
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=20150717105110.GL18994@arm.com \
--to=will.deacon@arm.com \
--cc=linux-arm-kernel@lists.infradead.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).