From: marc.zyngier@arm.com (Marc Zyngier)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCHv5 15/16] ARM: hyp: initialize CNTVOFF to zero
Date: Fri, 01 Feb 2013 11:43:23 +0000 [thread overview]
Message-ID: <510BAA5B.2060704@arm.com> (raw)
In-Reply-To: <20130201111350.GA1970@linaro.org>
Hi Dave,
On 01/02/13 11:13, Dave Martin wrote:
> On Thu, Jan 31, 2013 at 12:15:38PM +0000, Mark Rutland wrote:
>> From: Marc Zyngier <Marc.Zyngier@arm.com>
>>
>> In order to be able to use the virtual counter in a safe way,
>> make sure it is initialized to zero before dropping to SVC.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
>> Cc: Dave Martin <dave.martin@arm.com>
>> ---
>> arch/arm/kernel/hyp-stub.S | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
>> index 65b2417..455603a 100644
>> --- a/arch/arm/kernel/hyp-stub.S
>> +++ b/arch/arm/kernel/hyp-stub.S
>> @@ -152,6 +152,9 @@ THUMB( orr r7, #(1 << 30) ) @ HSCTLR.TE
>> mrc p15, 4, r7, c14, c1, 0 @ CNTHCTL
>> orr r7, r7, #3 @ PL1PCEN | PL1PCTEN
>> mcr p15, 4, r7, c14, c1, 0 @ CNTHCTL
>> + mov r6, #0
>> + mov r7, #0
>> + mcrr p15, 4, r6, r7, c14 @ CNTVOFF
>
> Is this required for safety, or is it more a sanity feature?
>
> The architected timer counters are supposed to be monotonic time sources
> only, so applying a random offset shouldn't really change anything.
>
> The main thing I can think of is that it is easier for the host to
> manage guests' virtual counter offsets if the host's offset is 0 (and
> we don't really want to be changing the host offset after the host kernel
> boots).
As you noticed, the offset itself doesn't matter as long as it is
constant. However, setting it to zero makes it nicer to the hypervisor:
no need to remember the host offset, just reset it to zero when exiting
a guest.
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2013-02-01 11:43 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-31 12:15 [PATCHv5 00/16] Unify arm_generic and arch_timer drivers Mark Rutland
2013-01-31 12:15 ` [PATCHv5 01/16] arm: arch_timer: balance device_node refcounting Mark Rutland
2013-01-31 15:33 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 02/16] arm: arch_timer: remove redundant available check Mark Rutland
2013-01-31 12:15 ` [PATCHv5 03/16] arm: arch_timer: use u64/u32 for register data Mark Rutland
2013-01-31 12:15 ` [PATCHv5 04/16] arm: arch_timer: standardise counter reading Mark Rutland
2013-01-31 15:34 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 05/16] arm: arch_timer: split cntfrq accessor Mark Rutland
2013-01-31 12:15 ` [PATCHv5 06/16] arm: arch_timer: factor out register accessors Mark Rutland
2013-01-31 12:15 ` [PATCHv5 07/16] arm: arch_timer: add isbs to " Mark Rutland
2013-01-31 15:35 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 08/16] arm: arch_timer: divorce from local_timer api Mark Rutland
2013-01-31 12:15 ` [PATCHv5 09/16] arm: arch_timer: add arch_counter_set_user_access Mark Rutland
2013-01-31 15:36 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 10/16] arm: arch_timer: move core to drivers/clocksource Mark Rutland
2013-01-31 12:15 ` [PATCHv5 11/16] arm64: arm_generic: prevent reading stale time Mark Rutland
2013-01-31 15:36 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 12/16] arm64: move from arm_generic to arm_arch_timer Mark Rutland
2013-01-31 12:15 ` [PATCHv5 13/16] Documentation: Add ARMv8 to arch_timer devicetree Mark Rutland
2013-01-31 12:15 ` [PATCHv5 14/16] ARM: arch_timers: switch to physical timers if HYP mode is available Mark Rutland
2013-01-31 15:37 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 15/16] ARM: hyp: initialize CNTVOFF to zero Mark Rutland
2013-02-01 11:13 ` Dave Martin
2013-02-01 11:43 ` Marc Zyngier [this message]
2013-02-01 11:46 ` Mark Rutland
2013-02-01 18:07 ` Dave Martin
2013-02-04 9:29 ` Mark Rutland
2013-01-31 12:15 ` [PATCHv5 16/16] clocksource: arch_timer: use virtual counters Mark Rutland
2013-01-31 15:38 ` Catalin Marinas
2013-01-31 17:39 ` [PATCHv5 00/16] Unify arm_generic and arch_timer drivers Stephen Warren
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