Re: [PATCH] do not p2m_invalidate_root when iommu_use_hap_pt

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 4 Aug 2021, Julien Grall wrote:
> Hi Stefano,
> 
> On 04/08/2021 01:08, Stefano Stabellini wrote:
> > > > diff --git a/xen/arch/arm/arm64/vsysreg.c b/xen/arch/arm/arm64/vsysreg.c
> > > > index caf17174b8..125a9281fc 100644
> > > > --- a/xen/arch/arm/arm64/vsysreg.c
> > > > +++ b/xen/arch/arm/arm64/vsysreg.c
> > > > @@ -105,6 +105,13 @@ void do_sysreg(struct cpu_user_regs *regs,
> > > >        case HSR_SYSREG_DCISW:
> > > >        case HSR_SYSREG_DCCSW:
> > > >        case HSR_SYSREG_DCCISW:
> > > > +        if ( iommu_use_hap_pt(current->domain) )
> > > > +        {
> > > > +            gdprintk(XENLOG_ERR,
> > > > +                     "d%u uses set/way cache flushes with the IOMMU on.
> > > > It
> > > > cannot work. Replace set/way instructions with dc [ci]vac and retry.
> > > > Injecting exception into the guest now.\n",
> > > 
> > > This line would be far too long to print on the serial. I think you want
> > > to
> > > add a few newline here.
> > 
> > Fair enough but I'll try to keep most info on the same line because
> > otherwise with a dom0less boot it can get confusing. I suggest:
> 
> I am not quite too sure to understand why it would get confusing with
> dom0less. Can you give an example?

I was doing tests with the error messages before implementing the undef
exception injection. This is the output of a regular domU (not
dom0less): https://pastebin.com/Wytg660j

The entire message in this test should be:

(XEN) d1v0 uses set/way cache flushes with the IOMMU on. It cannot work.
(XEN) Replace them with dc [ci]vac and retry.

But actually the first line gets eaten, so we only see:

(XEN) Replace them with dc [ci]vac and retry.

several times at the bottom of the logs.