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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [RFC][PATCH] KVM: Introduce modification context for cpu_synchronize_state |
Date: | Fri, 29 Jan 2010 08:50:53 -0600 |
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On 01/27/2010 08:54 AM, Jan Kiszka wrote:
This patch originates in the mp_state writeback issue: During runtime and even on reset, we must not write the previously saved VCPU state back into the kernel in an uncontrolled fashion. E.g mp_state should only written on reset or on VCPU setup. Certain clocks (e.g. the TSC) may only be written on setup or after vmload. By introducing additional information about the context of the planned vcpu state manipulation, we can simply skip sensitive states like mp_state when updating the in-kernel state. The planned modifications are defined when calling cpu_synchronize_state. They accumulate, ie. once a full writeback was requested, it will stick until it was performed. This patch already fixes existing writeback issues in upstream KVM by only selectively writing MSR_IA32_TSC, MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK, the mp_state and the vcpu_events. Signed-off-by: Jan Kiszka<address@hidden>
I think the context argument makes the function very difficult to call correctly.
I'd suggest making CPU_MODIFY_RUNTIME the behaviour of cpu_synchronize_state. I'd suggest adding another function to handle init like cpu_init_state(). Likewise, if an explicit reset state is needed, I think a cpu_init_state_after_reset() makes sense.
I don't quite understand the context that NONE should be used in.I think the key point though is to handle RUNTIME mostly transparently since it's the most common case.
Regards, Anthony Liguori
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