> -----Original Message-----
> From: Julien Grall <julien.gr...@arm.com>
> Sent: 26 September 2019 10:13
> To: Paul Durrant <paul.durr...@citrix.com>; 'Oleksandr'
> <olekst...@gmail.com>; 'Jan Beulich'
> <jbeul...@suse.com>
> Cc: nd <n...@arm.com>; Petre Pircalabu <ppircal...@bitdefender.com>; Stefano
> Stabellini
> <sstabell...@kernel.org>; Wei Liu <w...@xen.org>; KonradRzeszutek Wilk
> <konrad.w...@oracle.com>; Andrew
> Cooper <andrew.coop...@citrix.com>; David Scott <d...@recoil.org>; Tim
> (Xen.org) <t...@xen.org>; George
> Dunlap <george.dun...@citrix.com>; Tamas K Lengyel <ta...@tklengyel.com>; Ian
> Jackson
> <ian.jack...@citrix.com>; Anthony Perard <anthony.per...@citrix.com>;
> xen-devel@lists.xenproject.org;
> Volodymyr Babchuk <volodymyr_babc...@epam.com>; Roger Pau Monne
> <roger....@citrix.com>
> Subject: Re: [Xen-devel] [PATCH v13 0/4] add per-domain IOMMU control
>
> Hi,
>
> On 9/26/19 9:39 AM, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Julien Grall <julien.gr...@arm.com>
> >> Sent: 25 September 2019 22:34
> >> To: Paul Durrant <paul.durr...@citrix.com>; 'Oleksandr'
> >> <olekst...@gmail.com>; 'Jan Beulich'
> >> <jbeul...@suse.com>
> >> Cc: nd <n...@arm.com>; Petre Pircalabu <ppircal...@bitdefender.com>;
> >> Stefano Stabellini
> >> <sstabell...@kernel.org>; Wei Liu <w...@xen.org>; KonradRzeszutek Wilk
> >> <konrad.w...@oracle.com>;
> Andrew
> >> Cooper <andrew.coop...@citrix.com>; David Scott <d...@recoil.org>; Tim
> >> (Xen.org) <t...@xen.org>;
> George
> >> Dunlap <george.dun...@citrix.com>; Tamas K Lengyel <ta...@tklengyel.com>;
> >> Ian Jackson
> >> <ian.jack...@citrix.com>; Anthony Perard <anthony.per...@citrix.com>; xen-
> de...@lists.xenproject.org;
> >> Volodymyr Babchuk <volodymyr_babc...@epam.com>; Roger Pau Monne
> >> <roger....@citrix.com>
> >> Subject: Re: [Xen-devel] [PATCH v13 0/4] add per-domain IOMMU control
> >>
> >> Hi,
> >>
> >> On 25/09/2019 17:10, Paul Durrant wrote:
> >>>> -----Original Message-----
> >>>> From: Oleksandr <olekst...@gmail.com>
> >>>> Sent: 25 September 2019 16:50
> >>>> To: Paul Durrant <paul.durr...@citrix.com>; 'Jan Beulich'
> >>>> <jbeul...@suse.com>
> >>>> Cc: Petre Pircalabu <ppircal...@bitdefender.com>; Stefano Stabellini
> >>>> <sstabell...@kernel.org>;
> Wei
> >> Liu
> >>>> <w...@xen.org>; KonradRzeszutek Wilk <konrad.w...@oracle.com>; Andrew
> >>>> Cooper
> >>>> <andrew.coop...@citrix.com>; David Scott <d...@recoil.org>; Tim
> >>>> (Xen.org) <t...@xen.org>; George
> >> Dunlap
> >>>> <george.dun...@citrix.com>; Tamas K Lengyel <ta...@tklengyel.com>; Ian
> >>>> Jackson
> >>>> <ian.jack...@citrix.com>; Anthony Perard <anthony.per...@citrix.com>;
> >>>> xen-
> >> de...@lists.xenproject.org;
> >>>> Volodymyr Babchuk <volodymyr_babc...@epam.com>; Roger Pau Monne
> >>>> <roger....@citrix.com>; Julien
> >> Grall
> >>>> <julien.gr...@arm.com>
> >>>> Subject: Re: [Xen-devel] [PATCH v13 0/4] add per-domain IOMMU control
> >>>>
> >>>>
> >>>> [CC Julien]
> >>>>
> >>>>
> >>>> Hi Paul
> >>>>
> >>>> I may mistake, but looks like
> >>>>
> >>>> 80ff3d338dc93260b41ffeeebb0f852c2edef9ce iommu: tidy up
> >>>> iommu_use_hap_pt() and need_iommu_pt_sync() macros
> >>>>
> >>>> triggers ASSERT_UNREACHABLE on Arm if no IOMMU has been found (I built
> >>>> with my platform's IOMMU driver disabled: # CONFIG_IPMMU_VMSA is not
> >>>> set) .
> >>>>
> >>>> So, iommu_setup() calls clear_iommu_hap_pt_share() with
> >>>> iommu_hap_pt_share being set (CONFIG_IOMMU_FORCE_PT_SHARE=y) which,
> >>>> actually, triggers ASSERT.
> >>>>
> >>>
> >>> Here a minimal patch, leaving 'force pt share' in place. Does this avoid
> >>> the problem?
> >>>
> >>> ---8<---
> >>> diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
> >>> index e8763c7fdf..f88a285e7f 100644
> >>> --- a/xen/common/sysctl.c
> >>> +++ b/xen/common/sysctl.c
> >>> @@ -268,9 +268,11 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t)
> >>> u_sysctl)
> >>> pi->max_mfn = get_upper_mfn_bound();
> >>> arch_do_physinfo(pi);
> >>> if ( iommu_enabled )
> >>> + {
> >>> pi->capabilities |= XEN_SYSCTL_PHYSCAP_directio;
> >>> - if ( iommu_hap_pt_share )
> >>> - pi->capabilities |= XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share;
> >>> + if ( iommu_hap_pt_share )
> >>> + pi->capabilities |=
> >>> XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share;
> >>> + }
> >>>
> >>> if ( copy_to_guest(u_sysctl, op, 1) )
> >>> ret = -EFAULT;
> >>> diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
> >>> index 7c3003f3f1..6a10a24128 100644
> >>> --- a/xen/include/xen/iommu.h
> >>> +++ b/xen/include/xen/iommu.h
> >>> @@ -68,8 +68,6 @@ static inline void clear_iommu_hap_pt_share(void)
> >>> {
> >>> #ifndef iommu_hap_pt_share
> >>> iommu_hap_pt_share = false;
> >>> -#elif iommu_hap_pt_share
> >>> - ASSERT_UNREACHABLE();
> >>> #endif
> >>
> >> IHMO, calling this function is a mistake on platform only supporting
> >> shared page-table so the ASSERT() should be kept here.
> >>
> >> This raises the question why the function is actually called from common
> >> code. iommu_hap_enabled() should technically not be used in any code if
> >> the IOMMU is not enabled/present. So what are you trying to prevent here?
> >
> > What I'm trying to prevent, on x86, is a situation where the iommu_enabled
> > == false but
> iommu_hap_pt_share == true.
>
> This is not entirely uncommon to have other variables gated by others.
> So what could happen if you have iommu_enabled == false and
> iommu_hap_pt_share == true on x86?
>
Well, I was hoping to avoid the nested if in sysctl.c.
> > I had, mistakenly, believed that iommu_enabled would never be false for ARM
> > but it seems this is not
> the case so that situation has to be tolerated. I guess, given the other hunk
> of my patch, I can
> actually leave the ASSERT in place and avoid making the call from common
> code, in which case the
> function ought to move into an x86 header as well.
>
> By "the function", do you mean clear_iommu_hap_pt_share?
Yes.
> If so, I think
> it should stay were it is. This is a generic function that might be
> re-used for other architecture in the future.
>
That seems like a bit of a long shot. If I remove the call from iommu_setup()
then the only remaining callers are in x86 code, but I suppose it can stay
where it is to avoid the churn. I'll spin a new test patch.
Paul
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