Re: [Xen-devel] [PATCH 3/5] xen/smp: Update pv_lock_ops functions before alternative code starts under PVHVM

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 07/09/13 14:46, Konrad Rzeszutek Wilk wrote:
> Before this patch we would patch all of the pv_lock_ops sites
> using alternative assembler. Then later in the bootup cycle
> change the unlock_kick and lock_spinning to the Xen specific -
> without re patching.
> 
> That meant that for the core of the kernel we would be running
> with the baremetal version of unlock_kick and lock_spinning while
> for modules we would have the proper Xen specific slowpaths.
> 
> As most of the module uses some API from the core kernel that ended
> up with slowpath lockers waiting forever to be kicked (b/c they
> would be using the Xen specific slowpath logic). And the
> kick never came b/c the unlock path that was taken was the
> baremetal one.
> 
> On PV we do not have the problem as we initialise before the
> alternative code kicks in.
> 
> The fix is to move the updating of the pv_lock_ops function
> before the alternative code starts patching.

This comment seems odd.  The xen_spinlock_init() call is added not moved.

> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -731,4 +731,12 @@ void __init xen_hvm_smp_init(void)
>       smp_ops.cpu_die = xen_hvm_cpu_die;
>       smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
>       smp_ops.send_call_func_single_ipi = 
> xen_smp_send_call_function_single_ipi;
> +
> +     /*
> +      * The alternative logic (which patches the unlock/lock) runs before
> +      * the smp bootup up code is activated. That meant we would never patch
> +      * the core of the kernel with proper paravirt interfaces but would 
> patch
> +      * modules.
> +      */
> +     xen_init_spinlocks();

PV does this in xen_smp_prepare_boot_cpu.  It would be better if the
PVHVM case followed this same pattern and provide a smp_prepare_boot_cpu
implementation to do this?

David

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