Re: [Xen-devel] [PATCH 2 of 4] xenpaging: use wait queues

[Tim Deegan <tim@xxxxxxx>]

Hi, 

Is there a more recent version of this patch?  I see a newer version of
the wait-queues-for-mem-events one but not of this.

At 12:09 +0100 on 01 Dec (1322741358), Olaf Hering wrote:
> # HG changeset patch
> # User Olaf Hering <olaf@xxxxxxxxx>
> # Date 1322737507 -3600
> # Node ID 8147822efdee65d1f5b94656ab2032aedb76979f
> # Parent  612f69531fd15cf59c58404f6e4762733a9a268c
> xenpaging: use wait queues
> 
> Use a wait queue to put a guest vcpu to sleep while the requested gfn is
> in paging state. This adds missing p2m_mem_paging_populate() calls to
> some callers of the new get_gfn* variants, which would crash now
> because they get an invalid mfn. It also fixes guest crashes due to
> unexpected returns from do_memory_op because copy_to/from_guest ran into
> a paged gfn. Now those places will always get a valid mfn.
> 
> Since each gfn could be requested by several guest vcpus at the same
> time a queue of paged gfns is maintained. Each vcpu will be attached to
> that queue. Once p2m_mem_paging_resume restored the gfn the waiting
> vcpus will resume execution.
> 
> There is untested code in p2m_mem_paging_init_queue() to allow cpu
> hotplug. Since each vcpu may wait on a different gfn there have to be as
> many queues as vcpus. But xl vcpu-set does not seem to work right now,
> so this code path cant be excercised right now.
> 
> 
> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> 
> diff -r 612f69531fd1 -r 8147822efdee xen/arch/x86/hvm/hvm.c
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -454,6 +454,8 @@ int hvm_domain_initialise(struct domain 
>      spin_lock_init(&d->arch.hvm_domain.irq_lock);
>      spin_lock_init(&d->arch.hvm_domain.uc_lock);
>  
> +    spin_lock_init(&d->arch.hvm_domain.gfn_lock);
> +

I agree with Andres's comments on this lock, and will go futher: please
 - add it to the mm-locks.h system so we see any ordering vioations
   in future patches. 
 - add a detailed comment there explaining what exactly this lock protects.

Cheers,

Tim.

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