Re: [Xen-devel] [query] gic_set_lr always uses maintenance Interrupt

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-10-30 at 15:08 +0530, Mj Embd wrote:
> Hi,
> 
> As per section 5.2.2 of IHI0048B_b_gic_architecture_specification, If
> hypervisor is injecting a VIRQ into guest, that is actually a HW IRQ,

Is it? You mean LR.HW is set? AIUI this means the IRQ is an actual
hardware IRQ which is passed through, whereas the VIRQs are entirely
fictional virtual interrupts. (or maybe you mean some other sort of
VIRQ?)

> and guest does EOI (provided conditions) the maintenance interrupt is
> not needed.
> 
> In xen arch/arm/gic.c always while setting an LR using gic_set_lr ,
> the maintenance_int is enabled.
> 
> Can some one clear the doubt on why it is done
> a) is this because EOI by guest would result in control back to
> hypervisor to replenish the LR for   inflight, as there is otherwise
> no way to know in hypervisor that the LR is available.
> or
> b) some other reason ?

CCing Stefano, he understands this stuff and IIRC there was some reason
your a) didn't work in practice.

Ian.


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