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Re: [Qemu-devel] [PATCH] spapr/xive: H_INT_ESB is used for LSIs only

From: David Gibson
Subject: Re: [Qemu-devel] [PATCH] spapr/xive: H_INT_ESB is used for LSIs only
Date: Mon, 1 Jul 2019 17:56:45 +1000
User-agent: Mutt/1.12.0 (2019-05-25)

On Mon, Jul 01, 2019 at 07:55:03AM +0200, Cédric Le Goater wrote:
> On 01/07/2019 07:07, David Gibson wrote:
> > On Fri, Jun 21, 2019 at 05:05:45PM +0200, Cédric Le Goater wrote:
> >> On 21/06/2019 16:52, Greg Kurz wrote:
> >>> As indicated in the function header, this "hcall is only supported for
> >>> LISNs that have the ESB hcall flag set to 1 when returned from hcall()
> >>> H_INT_GET_SOURCE_INFO". We only set that flag for LSIs actually.
> >>>
> >>> Check that in h_int_esb().
> >>
> >> Indeed. H_INT_ESB should work on any IRQ, but I think it's better 
> >> to check that the HCALL is only used with the IRQ requiring it.
> > 
> > I'm not so convinced.  It seems to me that specifically limiting this
> > to certain things limits our options if we ever need future
> > workarounds for problems with ESB mapping.
> > 
> > In addition using H_INT_ESB for non-LSIs could be useful for minimal
> > guests (e.g. kvm-unit-tests) where mapping memory might be awkward.
> Ah yes. This is true. There is no real reason for enforcing this
> restriction in QEMU as H_INT_ESB should work on any irq. We can
> keep it that way I guess. It would be a small deviation from PAPR.

True, but "unexpectedly working" is a form of variation exceedingly
unlikely to break anything.

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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