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SubjectRe: [PATCH v2 7/7] iommu/vt-d: Consolidate domain_init() to avoid duplication
On Fri, 19 Jul 2019 16:27:04 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:

> Hi Alex,
>
> On 7/19/19 7:16 AM, Alex Williamson wrote:
> > On Wed, 12 Jun 2019 08:28:51 +0800
> > Lu Baolu <baolu.lu@linux.intel.com> wrote:
> >
> >> The domain_init() and md_domain_init() do almost the same job.
> >> Consolidate them to avoid duplication.
> >>
> >> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> >> ---
> >> drivers/iommu/intel-iommu.c | 123 +++++++++++-------------------------
> >> 1 file changed, 36 insertions(+), 87 deletions(-)
> >>
> >> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> >> index 5215dcd535a1..b8c6cf1d5f90 100644
> >> --- a/drivers/iommu/intel-iommu.c
> >> +++ b/drivers/iommu/intel-iommu.c
> >> @@ -1825,63 +1825,6 @@ static inline int guestwidth_to_adjustwidth(int gaw)
> >> return agaw;
> >> }
> >>
> >> -static int domain_init(struct dmar_domain *domain, struct intel_iommu *iommu,
> >> - int guest_width)
> >> -{
> >> - int adjust_width, agaw;
> >> - unsigned long sagaw;
> >> - int err;
> >> -
> >> - init_iova_domain(&domain->iovad, VTD_PAGE_SIZE, IOVA_START_PFN);
> >> -
> >> - err = init_iova_flush_queue(&domain->iovad,
> >> - iommu_flush_iova, iova_entry_free);
> >> - if (err)
> >> - return err;
> >> -
> >> - domain_reserve_special_ranges(domain);
> >> -
> >> - /* calculate AGAW */
> >> - if (guest_width > cap_mgaw(iommu->cap))
> >> - guest_width = cap_mgaw(iommu->cap);
> >> - domain->gaw = guest_width;
> >> - adjust_width = guestwidth_to_adjustwidth(guest_width);
> >> - agaw = width_to_agaw(adjust_width);
> >> - sagaw = cap_sagaw(iommu->cap);
> >> - if (!test_bit(agaw, &sagaw)) {
> >> - /* hardware doesn't support it, choose a bigger one */
> >> - pr_debug("Hardware doesn't support agaw %d\n", agaw);
> >> - agaw = find_next_bit(&sagaw, 5, agaw);
> >> - if (agaw >= 5)
> >> - return -ENODEV;
> >> - }
> >> - domain->agaw = agaw;
> >> -
> >> - if (ecap_coherent(iommu->ecap))
> >> - domain->iommu_coherency = 1;
> >> - else
> >> - domain->iommu_coherency = 0;
> >> -
> >> - if (ecap_sc_support(iommu->ecap))
> >> - domain->iommu_snooping = 1;
> >> - else
> >> - domain->iommu_snooping = 0;
> >> -
> >> - if (intel_iommu_superpage)
> >> - domain->iommu_superpage = fls(cap_super_page_val(iommu->cap));
> >> - else
> >> - domain->iommu_superpage = 0;
> >> -
> >> - domain->nid = iommu->node;
> >> -
> >> - /* always allocate the top pgd */
> >> - domain->pgd = (struct dma_pte *)alloc_pgtable_page(domain->nid);
> >> - if (!domain->pgd)
> >> - return -ENOMEM;
> >> - __iommu_flush_cache(iommu, domain->pgd, PAGE_SIZE);
> >> - return 0;
> >> -}
> >> -
> >> static void domain_exit(struct dmar_domain *domain)
> >> {
> >> struct page *freelist;
> >> @@ -2563,6 +2506,31 @@ static int get_last_alias(struct pci_dev *pdev, u16 alias, void *opaque)
> >> return 0;
> >> }
> >>
> >> +static int domain_init(struct dmar_domain *domain, int guest_width)
> >> +{
> >> + int adjust_width;
> >> +
> >> + init_iova_domain(&domain->iovad, VTD_PAGE_SIZE, IOVA_START_PFN);
> >> + domain_reserve_special_ranges(domain);
> >> +
> >> + /* calculate AGAW */
> >> + domain->gaw = guest_width;
> >> + adjust_width = guestwidth_to_adjustwidth(guest_width);
> >> + domain->agaw = width_to_agaw(adjust_width);
> >
> >
> > How do we justify that domain->agaw is nothing like it was previously
> > here? I spent some more time working on the failure to boot that I
> > thought was caused by 4ec066c7b147, but there are so many breakages and
> > fixes in Joerg's x86/vt-d branch that I think my bisect zero'd in on
> > the wrong one. Instead I cherry-picked every commit from Joerg's tree
> > and matched Fixes patches to their original commit, which led me to
> > this patch, mainline commit 123b2ffc376e. The issue I'm seeing is that
> > we call domain_context_mapping_one() and we are in this section:
> >
> > struct dma_pte *pgd = domain->pgd;
> > int agaw;
> >
> > context_set_domain_id(context, did);
> >
> > if (translation != CONTEXT_TT_PASS_THROUGH) {
> > /*
> > * Skip top levels of page tables for iommu which has
> > * less agaw than default. Unnecessary for PT mode.
> > */
> > for (agaw = domain->agaw; agaw > iommu->agaw; agaw--) {
> > ret = -ENOMEM;
> > pgd = phys_to_virt(dma_pte_addr(pgd));
> > if (!dma_pte_present(pgd))
> > goto out_unlock;
> > }
> >
> > Prior to this commit, we had domain->agaw=1 and iommu->agaw=1, so we
> > don't enter the loop. With this commit, we have domain->agaw=3,
> > iommu->agaw=1 with pgd->val=0!
> >
>
> iommu->agaw presents the level of page table which is by default
> supported by the @iommu. domain->agaw presents the level of page
> table which is used by the @domain.
>
> agaw = 1: 3-level page table
> agaw = 2: 4-level page table
> agaw = 3: 5-level page table
>
> The case here is that @iommu only supports 3-level page table, but the
> @domain was set to use 5-level page table. So we must skip level 4 and 5
> page tables of the @domain.
>
> This code in the loop looks odd to me. It will always goto to unlock and
> leave pgd->val==0. How about below change? (not tested yet!)
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 412f18aba501..98d6878cd29d 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2020,11 +2020,15 @@ static int domain_context_mapping_one(struct
> dmar_domain *domain,
> * Skip top levels of page tables for iommu
> which has
> * less agaw than default. Unnecessary for PT mode.
> */
> - for (agaw = domain->agaw; agaw > iommu->agaw;
> agaw--) {
> - ret = -ENOMEM;
> - pgd = phys_to_virt(dma_pte_addr(pgd));
> - if (!dma_pte_present(pgd))
> - goto out_unlock;
> + while (iommu->agaw < domain->agaw) {
> + struct dma_pte *pte;
> +
> + pte = domain->pgd;
> + if (dma_pte_present(pte)) {
> + domain->pgd =
> phys_to_virt(dma_pte_addr(pte));
> + free_pgtable_page(pte);
> + }
> + domain->agaw--;
> }
>
> info = iommu_support_dev_iotlb(domain, iommu,
> bus, devfn);


The system still fails to boot, now with DMAR faults indicating invalid
context entry.

> > I don't really follow how the setting of these fields above is
> > equivalent to what they were previously or if they're supposed to be
> > updated lazily, but the current behavior is non-functional. Commit
> > 123b2ffc376e can be reverted with only a bit of offset, which brings
> > Linus' tree back into working operation for me. Should we revert or is
> > there an obvious fix here? Thanks,
>
> This commit is not the root cause of this issue as far as I can see, it
> only triggers above loop to get entered.

The system fails to boot with this commit, it does boot without this
commit. Whether this commit exposed a latent issue or introduced a bug
itself is academic. Thanks,

Alex

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