Re: [PATCH for-9.2 v6 03/12] hw/riscv: add RISC-V IOMMU base emulation

[Andrew Jones <ajones@ventanamicro.com>]

On Tue, Oct 01, 2024 at 09:05:52PM GMT, Daniel Henrique Barboza wrote:
> 
> 
> On 10/1/24 8:28 PM, Tomasz Jeznach wrote:
> > On Tue, Sep 3, 2024 at 4:46 AM Daniel Henrique Barboza
> > <dbarboza@ventanamicro.com> wrote:
> > > 
> > > 
> > > 
> > > On 8/26/24 11:18 PM, Tomasz Jeznach wrote:
> > > > On Fri, Aug 23, 2024 at 5:42 AM Daniel Henrique Barboza
> > > > <dbarboza@ventanamicro.com> wrote:
> > > > > 
> > > > > 
> > > > > 
> > > > > On 8/20/24 12:16 PM, Jason Chien wrote:
> > > > > > Hi Daniel,
> > > > > > 
> 
> (...)
> 
> > > >            iotlb->target_as = &s->trap_as;
> > > > 
> > > > I'd suggest fixing the missing en_s check, to enable proper handling of MSIP.
> > > 
> > > The '!en_s' check was removed because it was breaking irqbypass. I'll let Drew explain
> > > more about it since he's been working in the kernel support for this use case.
> > > 
> > > 
> > 
> > Is the missing `!en_s` check still problematic?
> > Re-reading the code I'd say it's required here to catch only GPAs if S
> > stage is BARE, not untranslated IOVA.
> 
> 
> Yeah, for some reason the existence of that check  breaks irqbypass, removing
> it fixes it.
> 
> I don't think it has to do with the check per se, but perhaps with a missing
> conditional to proper handle the irqbypass case. This is one of the TODOs that
> we should look at later, in particular when the irqbypass support starts to
> get reviewed in the kernel.

Right. VFIO only uses S-stage to translate GPAs. When irqbypass support
is added, as it is here [1] (which is a series I've been waiting to post
as an RFC after the first round of IOMMU driver patches gets merged),
then this '!en_s' check breaks MSI translations.

Thanks,
drew