linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
From: marc.zyngier@arm.com (Marc Zyngier)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 3/4] Add physical count arch timer support for clocksource in ARMv7.
Date: Fri, 13 Sep 2013 14:40:29 +0100	[thread overview]
Message-ID: <523315CD.8010704@arm.com> (raw)
In-Reply-To: <CAK3cCBw4EKypLmhf4L5_P3d27QzsrB+ZxUTgF58YhmUhBa00xQ@mail.gmail.com>

On 13/09/13 14:09, cinifr wrote:
>> I urge you to read the ARM ARM, and specifically the section dedicated
>> to trapping access to CP15 operations. If you do, you'll quickly notice
>> that you *cannot* trap accesses to the timer subsystem.
>>
> I read it again. The ARMv7 manual said "Is accessible from Non-secure
> PL1 modes only when CNTHCTL.PL1PCTEN is set to 1. When
> CNTHCTL.PL1PCTEN is set to 0, any attempt to access CNTPCT from a
> Non-secure PL1 mode ***generates a Hyp Trap exception***, see Hyp Trap
> exception on page B1-1206" in B8.1.2. but I dont find  a  special hyp
> trap control  for accessing CNTPCT in manual. As you said HSTR cannot
> trap accessing of CP15 c14. What happer when OS access CNTPCT from PL1
> NS=1 mode with CNTHCTL.PL1PCTEN=0 ???  AmI  wrong for understanding
> the manual?

That's interesting, as I never noticed this particular line in the ARM
ARM. I'll investigate this, thanks for bringing it up.

This doesn't change the fact that using the physical timer/counter in a
VM is (or can be) horribly expensive, and should be avoided at all cost.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

  reply	other threads:[~2013-09-13 13:40 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-09-12  6:51 [PATCH 0/4] Add smp support for Allwinner A20 and phy arch count timer Fan Rong
2013-09-12  6:51 ` [PATCH 1/4] Add smp support for Allwinner A20(sunxi 7i) Fan Rong
2013-09-12 14:26   ` Mark Rutland
2013-09-12 15:53     ` cinifr
2013-09-12 14:40   ` Russell King - ARM Linux
2013-09-12  6:51 ` [PATCH 2/4] Add cpuconfig nodes in dts for smp configure Fan Rong
2013-09-14 11:50   ` Maxime Ripard
2013-09-12  6:51 ` [PATCH 3/4] Add physical count arch timer support for clocksource in ARMv7 Fan Rong
2013-09-12 11:24   ` Mark Rutland
2013-09-12 14:33     ` Russell King - ARM Linux
2013-09-12 16:09       ` cinifr
2013-09-12 15:39     ` [linux-sunxi] " Ian Campbell
2013-09-12 16:07     ` cinifr
2013-09-12 16:39       ` Marc Zyngier
2013-09-13  8:49         ` cinifr
2013-09-13  9:30           ` Marc Zyngier
2013-09-13 13:09             ` cinifr
2013-09-13 13:40               ` Marc Zyngier [this message]
2013-09-13 14:55                 ` cinifr
2013-09-18  9:03                 ` cinifr
2013-09-14 12:05             ` maxime.ripard at free-electrons.com
2013-09-16  8:16               ` Marc Zyngier
2013-09-12  6:51 ` [PATCH 4/4] Add arch count timer node in dts for Allwinner A20(sunxi 7i) Fan Rong
2013-09-12 14:57   ` Mark Rutland
2013-09-12 15:44     ` [linux-sunxi] " Ian Campbell
2013-09-12 16:23       ` cinifr
2013-09-12 19:53         ` Henrik Nordström
2013-09-12 14:39 ` [PATCH 0/4] Add smp support for Allwinner A20 and phy arch count timer Mark Rutland
2013-09-12 15:46   ` cinifr
2013-09-13 11:20     ` Mark Rutland
2013-09-13 13:23       ` cinifr

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=523315CD.8010704@arm.com \
    --to=marc.zyngier@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).