From: Avi Kivity <avi@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: Jan Kiszka <jan.kiszka@web.de>, kvm@vger.kernel.org
Subject: Re: [PATCH] Don't call cpu_synchronize_state() in apic_init_reset()
Date: Thu, 24 Sep 2009 11:24:09 +0300 [thread overview]
Message-ID: <4ABB2CA9.1020403@redhat.com> (raw)
In-Reply-To: <20090924080312.GB9832@redhat.com>
On 09/24/2009 11:03 AM, Gleb Natapov wrote:
>>
>>> The new rule is: Synchronize the states before accessing registers (or
>>> in-kernel devices) the first time after a vmexit to user space.
>>>
>> No, the rule is: synchronize state before accessing registers.
>> Extra synchronization is cheap, while missing synchronization is
>> very expensive.
>>
>>
> So should we stick cpu_synchronize_state() before each register
> accesses? I think it is reasonable to omit it if all callers do it
> already.
>
If the callee is static we can and should avoid it. If the function is
exported then we shouldn't rely on callers.
IOW, it's fine to depend on local details (which a reader can easily
gain), but better to avoid depending on global details.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2009-09-24 8:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-22 14:51 [PATCH] Update halted state from mpstate only in case of inkernel irq chip Gleb Natapov
2009-09-22 14:51 ` [PATCH] Don't call kvm_cpu_synchronize_state() if there is no irqchip events to process Gleb Natapov
2009-09-23 9:00 ` Avi Kivity
2009-09-22 14:51 ` [PATCH] Don't call cpu_synchronize_state() in apic_init_reset() Gleb Natapov
2009-09-23 9:00 ` Avi Kivity
2009-09-23 15:07 ` Jan Kiszka
2009-09-23 15:17 ` Avi Kivity
2009-09-23 15:45 ` Jan Kiszka
2009-09-24 7:53 ` Avi Kivity
2009-09-24 8:03 ` Gleb Natapov
2009-09-24 8:15 ` Jan Kiszka
2009-09-24 8:30 ` Gleb Natapov
2009-09-24 8:59 ` Jan Kiszka
2009-09-24 9:11 ` Gleb Natapov
2009-09-25 15:03 ` Jan Kiszka
2009-09-24 8:24 ` Avi Kivity [this message]
2009-09-23 9:00 ` [PATCH] Update halted state from mpstate only in case of inkernel irq chip Avi Kivity
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