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[Qemu-devel] Re: [PATCH 2/9] qemu-kvm: Clean up register access API

From: Avi Kivity
Subject: [Qemu-devel] Re: [PATCH 2/9] qemu-kvm: Clean up register access API
Date: Sun, 21 Feb 2010 11:25:01 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100120 Fedora/3.0.1-1.fc12 Thunderbird/3.0.1

On 02/19/2010 08:22 PM, Jan Kiszka wrote:
qemu-kvm's functions for accessing the VCPU registers are
kvm_arch_load/save_regs. Use them directly instead of going through
various wrappers. Specifically, we do not need on_vcpu wrapping as all
users either already run in the related thread or call while the vm is
stopped. This is now also validated during runtime via asserts.

+    assert(kvm_cpu_is_stopped(env) || env->thread_id == kvm_get_thread_id());

The kvm_cpu_is_stopped() part is wrong, for two reasons. First, a future ABI revolution might switch to syscalls and thus make the association between vcpu and thread implicit. This will allow us to drop vcpu->mutex, eventually. Second, kvm_cpu_is_stopped() will be racy in a threaded future version of qemu. All vcpu ioctls should be made from the vcpu thread.

Documentation/kvm/api.txt has this to say about the matter:

 - vcpu ioctls: These query and set attributes that control the operation
   of a single virtual cpu.

   Only run vcpu ioctls from the same thread that was used to create the

So it isn't just me.

error compiling committee.c: too many arguments to function

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