Re: [Xen-devel] [PATCH] x86/shim: fix ballooning up the guest

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.03.2020 22:47, Igor Druzhinin wrote:
> args.preempted as meaningless here and doesn't show if the hypercall
> was preempted before. Use start_extent instead which is correct.

... as long as the hypercall was invoked in a "normal" way.

> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> ---
> This fixes ballooning for 64-bit PV guests inside shim. 32-bit PV guests
> require a little bit more work due to compat layer being involved.
> ---
>  xen/common/memory.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/common/memory.c b/xen/common/memory.c
> index 444c081..5fdd2a2 100644
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -1191,7 +1191,7 @@ long do_memory_op(unsigned long cmd, 
> XEN_GUEST_HANDLE_PARAM(void) arg)
>          }
>  
>  #ifdef CONFIG_X86
> -        if ( pv_shim && op != XENMEM_decrease_reservation && !args.preempted 
> )
> +        if ( pv_shim && op != XENMEM_decrease_reservation && !start_extent )
>              /* Avoid calling pv_shim_online_memory when preempted. */
>              pv_shim_online_memory(args.nr_extents, args.extent_order);

The code change can have my R-b, but I'd like the comment to also
be changed then - it shouldn't talk about preemption in the way
it does. Perhaps "... when this is a continuation"? I'd be okay
making this change while committing.

As an aside, it would probably have been a good idea to also Cc
Roger as the original author of this code.

Jan

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