Re: [Xen-devel] [PATCH v4 5/7] x86/hyperv: provide percpu hypercall input page

[Jan Beulich <jbeulich@suse.com>]

On 22.01.2020 21:23, Wei Liu wrote:
> --- a/xen/arch/x86/guest/hyperv/hyperv.c
> +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> @@ -27,7 +27,10 @@
>  #include <asm/guest/hyperv-tlfs.h>
>  #include <asm/processor.h>
>  
> +#include "private.h"
> +
>  struct ms_hyperv_info __read_mostly ms_hyperv;
> +DEFINE_PER_CPU_READ_MOSTLY(void *, hv_pcpu_input_arg);

Would it perhaps be helpful to make recognizable that this can hold
up to a page's worth of data, either by its type or by a slightly
different name?

> @@ -119,14 +122,36 @@ static void __init setup_hypercall_page(void)
>      }
>  }
>  
> +static void setup_hypercall_pcpu_arg(void)
> +{
> +    void *mapping;
> +
> +    if ( this_cpu(hv_pcpu_input_arg) )
> +        return;
> +
> +    mapping = alloc_xenheap_page();
> +    if ( !mapping )
> +        panic("Failed to allocate hypercall input page for CPU%u\n",
> +              smp_processor_id());

panic() is likely fine for the BSP, but I don't think any AP should
be able to bring down the system because of memory shortage. Such
an AP should simply not come online. (Even for the BSP the question
is whether Xen would be able to run despite failure here.)

Jan

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