Re: [Xen-devel] [PATCH v6 1/7] xen/x86: remove XENFEAT_hvm_pirqs for PVHv2 guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.02.17 at 13:33, <roger.pau@xxxxxxxxxx> wrote:
> --- a/docs/misc/hvmlite.markdown
> +++ b/docs/misc/hvmlite.markdown
> @@ -75,3 +75,23 @@ info structure that's passed at boot time (field 
> rsdp_paddr).
>  
>  Description of paravirtualized devices will come from XenStore, just as it's
>  done for HVM guests.
> +
> +## Interrupts ##
> +
> +### Interrupts from physical devices ###
> +
> +Interrupts from physical devices are delivered using native methods, this is
> +done in order to take advantage of new hardware assisted virtualization
> +functions, like posted interrupts. This implies that PVHv2 guests with 
> physical
> +devices will also have the necessary interrupt controllers in order to manage
> +the delivery of interrupts from those devices, using the same interfaces that
> +are available on native hardware.
> +
> +### Interrupts from paravirtualized devices ###
> +
> +Interrupts from paravirtualized devices are delivered using event channels, 
> see
> +[Event Channel Internals][event_channels] for more detailed information about
> +event channels. Delivery of those interrupts can be configured in the same 
> way
> +as HVM guests, check xen/include/public/hvm/params.h and
> +xen/include/public/hvm/hvm_op.h for more information about available delivery
> +methods.

Just FTR - my comments on v4 still stand; I especially don't buy
your argument [1] of posted interrupts becoming more widely
available, since - as pointed out before - we continue to not fully
enable their use by default, due to unresolved problems with
the implementation. Furthermore emulation_flags_ok() allows
EMU_LAPIC to be clear (together with all other bits being clear),
in which case posted interrupts can't be used at all afaict.

Jan

[1] https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg02092.html


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