Re: [PATCH] KVM: VMX: Fix repeatly allocate of apic access page

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Sheng Yang wrote:
> From 05164d73994a88ae130a086b592cd127c15a617f Mon Sep 17 00:00:00 2001
> From: Sheng Yang <sheng.yang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Date: Tue, 6 Nov 2007 11:37:44 +0800
> Subject: [PATCH] KVM: VMX: Fix repeatly allocate of apic access page
>
> For SMP guest, alloc_apic_access_page() would be called more than once.
> So only the last one works, causing SMP guest can't benifit from FlexPriority.
>
> This patch fixed this issue.
>
> Signed-off-by: Sheng Yang <sheng.yang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> ---
>  drivers/kvm/vmx.c |   14 ++++++++++----
>  1 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
> index 42e7fad..6670e2b 100644
> --- a/drivers/kvm/vmx.c
> +++ b/drivers/kvm/vmx.c
> @@ -1463,18 +1463,24 @@ static void seg_setup(int seg)
>  static int alloc_apic_access_page(struct kvm *kvm)
>  {
>  	struct kvm_userspace_memory_region kvm_userspace_mem;
> -	int r;
> +	int r = 0;
>  
> -	r = -EFAULT;
> +	mutex_lock(&kvm->lock);
> +	if (kvm->apic_access_page)
> +		goto out;
> +	mutex_unlock(&kvm->lock);
>   

Still racy.  I two threads create a vcpu at the same time, they can both 
reach this point simultaneously.

I suggest having a __kvm_set_memory_region() that does not take 
kvm->lock, and call that instead, so the whole thing can be done within 
a single lock.

>  	kvm_userspace_mem.slot = APIC_ACCESS_PAGE_PRIVATE_MEMSLOT;
>  	kvm_userspace_mem.flags = 0;
>  	kvm_userspace_mem.guest_phys_addr = 0xfee00000ULL;
>  	kvm_userspace_mem.memory_size = PAGE_SIZE;
>  	r = kvm_set_memory_region(kvm, &kvm_userspace_mem, 0);
>  	if (r)
> -		return r;
> +		goto out;
> +	mutex_lock(&kvm->lock);
>  	kvm->apic_access_page = gfn_to_page(kvm, 0xfee00);
> -	return 0;
> +out:
> +	mutex_unlock(&kvm->lock);
> +	return r;
>  }
>  
>   

-- 
error compiling committee.c: too many arguments to function


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