> -----Original Message-----
> From: Jan Beulich <jbeul...@suse.com>
> Sent: 07 August 2019 11:32
> To: Paul Durrant <paul.durr...@citrix.com>
> Cc: xen-devel@lists.xenproject.org; Julien Grall <julien.gr...@arm.com>;
> Alexandru Isaila
> <aisa...@bitdefender.com>; Petre Pircalabu <ppircal...@bitdefender.com>;
> Razvan Cojocaru
> <rcojoc...@bitdefender.com>; Andrew Cooper <andrew.coop...@citrix.com>; Roger
> Pau Monne
> <roger....@citrix.com>; VolodymyrBabchuk <volodymyr_babc...@epam.com>; George
> Dunlap
> <george.dun...@citrix.com>; Ian Jackson <ian.jack...@citrix.com>; Stefano
> Stabellini
> <sstabell...@kernel.org>; Konrad Rzeszutek Wilk <konrad.w...@oracle.com>;
> Tamas K Lengyel
> <ta...@tklengyel.com>; Tim (Xen.org) <t...@xen.org>; Wei Liu <w...@xen.org>
> Subject: Re: [Xen-devel] [PATCH 3/6] remove late (on-demand) construction of
> IOMMU page tables
>
> On 30.07.2019 15:44, Paul Durrant wrote:
> > NOTE: This patch will cause a small amount of extra resource to be used
> > to accommodate IOMMU page tables that may never be used, since the
> > per-domain IOMMU flag enable flag is currently set to the value
> > of the global iommu_enable flag. A subsequent patch will add an
> > option to the toolstack to allow it to be turned off if there is
> > no intention to assign passthrough hardware to the domain.
>
> In particular if the default of this is going to be "true" (I
> didn't look at that patch yet, but the wording above makes me
> assume so), in auto-ballooning mode without shared page tables
> more memory should imo be ballooned out of Dom0 now. It has
> always been a bug that IOMMU page tables weren't accounted for,
> but it would become even more prominent then.
Ultimately, once the whole series is applied, then nothing much should change
for those specifying passthrough h/w in an xl.cfg. The main difference will be
that h/w cannot be passed through to a domain that was not originally created
with IOMMU pagetables.
With patches applied up to this point then, yes, every domain will get IOMMU
page tables. I guess I'll take a look at the auto-ballooning code and see what
needs to be done.
>
> > --- a/xen/arch/x86/hvm/mtrr.c
> > +++ b/xen/arch/x86/hvm/mtrr.c
> > @@ -783,7 +783,8 @@ HVM_REGISTER_SAVE_RESTORE(MTRR, hvm_save_mtrr_msr,
> > hvm_load_mtrr_msr, 1,
> >
> > void memory_type_changed(struct domain *d)
> > {
> > - if ( (has_iommu_pt(d) || cache_flush_permitted(d)) && d->vcpu &&
> > d->vcpu[0] )
> > + if ( (is_iommu_enabled(d) || cache_flush_permitted(d)) && d->vcpu &&
> > + d->vcpu[0] )
>
> As a really minor comment - I think it wouldn't be bad for both
> d->vcpu references to end up on the same line.
Ok.
>
> > @@ -625,8 +548,7 @@ static void iommu_dump_p2m_table(unsigned char key)
> > ops = iommu_get_ops();
> > for_each_domain(d)
> > {
> > - if ( is_hardware_domain(d) ||
> > - dom_iommu(d)->status < IOMMU_STATUS_initialized )
> > + if ( !is_iommu_enabled(d) )
> > continue;
>
> Why do you drop the hwdom check here?
Because is_iommu_enabled() for the h/w domain will always be true if
iommu_enabled is true, so no need for a special case.
>
> > --- a/xen/include/asm-arm/iommu.h
> > +++ b/xen/include/asm-arm/iommu.h
> > @@ -21,7 +21,7 @@ struct arch_iommu
> > };
> >
> > /* Always share P2M Table between the CPU and the IOMMU */
> > -#define iommu_use_hap_pt(d) (has_iommu_pt(d))
> > +#define iommu_use_hap_pt(d) (is_iommu_enabled(d))
>
> I'd suggest dropping the stray outer pair of parentheses at the
> same time.
Ok, will do.
Paul
>
> Jan
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