Messages in this thread | | | Subject | Re: [PATCH] iommu/vt-d: Add side channel for huge page support to Intel IOMMU. | From | Lu Baolu <> | Date | Thu, 21 Nov 2019 09:18:52 +0800 |
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Hi Yonghyun,
Linux VT-d driver is developed and maintained according to VT-d spec rev3.0. I didn't find anything about super page support for ATS in the spec. I am not the spec maintainer so I have no idea about how the spec evolves.
Best regards, baolu
On 11/21/19 5:54 AM, Yonghyun Hwang wrote: > Hello Baolu, > > As far as I know, PCIe standard doesn't define a field for large page > attribution in a response message. This was the motivation to implement > the side channel. > > I think I could miss something on your proposal. Could you elaborate how > VT-d can be involved to include the large page attribution in the > response message? > > Kind regards, > Yonghyun > > On Tue, Nov 19, 2019 at 5:50 PM Lu Baolu <baolu.lu@linux.intel.com > <mailto:baolu.lu@linux.intel.com>> wrote: > > Hi, > > On 11/20/19 8:36 AM, Yonghyun Hwang wrote: > > PCIe Address Translation Service (ATS) allows a PCIe device to > look up > > VA->PA translations maintained by the IOMMU and cache them. The > IOMMU up > > until at least Skylake fractures all ATS responses into 4 KiB > pages, even > > if the underlying page is 2 MiB. For added performance, a side > channel is > > defined, which lets the device know if the page is actually a 2 > MiB page > > and uses that information instead of the ATS Response size > information to > > determine the actual page size to use. The side channel is mapped > to an > > unused high-order PA bit, 45-bit, that is transferred intact from > the IOMMU > > PTE to the device. > > BIT 45 of VT-d second level page table entry is not ignored but Reserved > (must be 0). (Spec 3.0 section 9.8). So it couldn't be used for software > purpose. > > I guess the right approach should be VT-d hardware involved. For > example, VT-d reads the PTE entry in response of an ATS request, and > check the large page attribution of this PTE then include the large page > information in the response. It's not a good idea to hide the response > information in the pfn and walk around VT-d hardware. > > Best regards, > baolu > > > > > Signed-off-by: Yonghyun Hwang <yonghyun@google.com > <mailto:yonghyun@google.com>> > > --- > > drivers/iommu/intel-iommu.c | 83 > ++++++++++++++++++++++++++++++++----- > > drivers/iommu/intel-pasid.c | 2 +- > > include/linux/intel-iommu.h | 37 ++++++++++++----- > > include/linux/iommu.h | 1 + > > 4 files changed, 102 insertions(+), 21 deletions(-) > > > > diff --git a/drivers/iommu/intel-iommu.c > b/drivers/iommu/intel-iommu.c > > index fe8097078669..f748985b8081 100644 > > --- a/drivers/iommu/intel-iommu.c > > +++ b/drivers/iommu/intel-iommu.c > > @@ -307,6 +307,9 @@ static int hw_pass_through = 1; > > */ > > #define DOMAIN_FLAG_LOSE_CHILDREN BIT(1) > > > > +/* Domain used for huge-page side channel. */ > > +#define DOMAIN_FLAG_A45_HUGE_PAGE (1 << 2) > > + > > #define for_each_domain_iommu(idx, domain) \ > > for (idx = 0; idx < g_num_of_iommus; idx++) \ > > if (domain->iommu_refcnt[idx]) > > @@ -552,6 +555,20 @@ static inline int domain_type_is_si(struct > dmar_domain *domain) > > return domain->flags & DOMAIN_FLAG_STATIC_IDENTITY; > > } > > > > +static inline void domain_type_set_a45_huge_page(struct > dmar_domain *domain, > > + bool huge_page) > > +{ > > + if (huge_page) > > + domain->flags |= DOMAIN_FLAG_A45_HUGE_PAGE; > > + else > > + domain->flags &= ~DOMAIN_FLAG_A45_HUGE_PAGE; > > +} > > + > > +inline bool domain_type_get_a45_huge_page(struct dmar_domain > *domain) > > +{ > > + return (domain->flags & DOMAIN_FLAG_A45_HUGE_PAGE) != 0; > > +} > > + > > static inline int domain_pfn_supported(struct dmar_domain *domain, > > unsigned long pfn) > > { > > @@ -922,7 +939,7 @@ static struct dma_pte *pfn_to_dma_pte(struct > dmar_domain *domain, > > if (level == 1) > > break; > > > > - parent = phys_to_virt(dma_pte_addr(pte)); > > + parent = phys_to_virt(dma_pte_addr(pte, domain)); > > level--; > > } > > > > @@ -958,7 +975,7 @@ static struct dma_pte > *dma_pfn_level_pte(struct dmar_domain *domain, > > return pte; > > } > > > > - parent = phys_to_virt(dma_pte_addr(pte)); > > + parent = phys_to_virt(dma_pte_addr(pte, domain)); > > total--; > > } > > return NULL; > > @@ -1012,7 +1029,7 @@ static void dma_pte_free_level(struct > dmar_domain *domain, int level, > > goto next; > > > > level_pfn = pfn & level_mask(level); > > - level_pte = phys_to_virt(dma_pte_addr(pte)); > > + level_pte = phys_to_virt(dma_pte_addr(pte, domain)); > > > > if (level > 2) { > > dma_pte_free_level(domain, level - 1, > retain_level, > > @@ -1073,7 +1090,7 @@ static struct page > *dma_pte_list_pagetables(struct dmar_domain *domain, > > { > > struct page *pg; > > > > - pg = pfn_to_page(dma_pte_addr(pte) >> PAGE_SHIFT); > > + pg = pfn_to_page(dma_pte_addr(pte, domain) >> PAGE_SHIFT); > > pg->freelist = freelist; > > freelist = pg; > > > > @@ -1125,7 +1142,8 @@ static struct page > *dma_pte_clear_level(struct dmar_domain *domain, int level, > > } else if (level > 1) { > > /* Recurse down into a level that isn't > *entirely* obsolete */ > > freelist = dma_pte_clear_level(domain, > level - 1, > > - > phys_to_virt(dma_pte_addr(pte)), > > + phys_to_virt( > > + > dma_pte_addr(pte, domain)), > > level_pfn, > start_pfn, last_pfn, > > freelist); > > } > > @@ -2063,7 +2081,7 @@ static int > domain_context_mapping_one(struct dmar_domain *domain, > > */ > > for (agaw = domain->agaw; agaw > > iommu->agaw; agaw--) { > > ret = -ENOMEM; > > - pgd = phys_to_virt(dma_pte_addr(pgd)); > > + pgd = > phys_to_virt(dma_pte_addr(pgd, domain)); > > if (!dma_pte_present(pgd)) > > goto out_unlock; > > } > > @@ -2229,6 +2247,9 @@ static int __domain_mapping(struct > dmar_domain *domain, unsigned long iov_pfn, > > unsigned long sg_res = 0; > > unsigned int largepage_lvl = 0; > > unsigned long lvl_pages = 0; > > + uint64_t large_page = DMA_PTE_LARGE_PAGE | > > + (domain_type_get_a45_huge_page(domain) ? > > + DMA_PTE_A45_HUGE_PAGE : 0); > > > > BUG_ON(!domain_pfn_supported(domain, iov_pfn + nr_pages - 1)); > > > > @@ -2265,7 +2286,7 @@ static int __domain_mapping(struct > dmar_domain *domain, unsigned long iov_pfn, > > if (largepage_lvl > 1) { > > unsigned long nr_superpages, end_pfn; > > > > - pteval |= DMA_PTE_LARGE_PAGE; > > + pteval |= large_page; > > lvl_pages = > lvl_to_nr_pages(largepage_lvl); > > > > nr_superpages = sg_res / lvl_pages; > > @@ -2280,7 +2301,7 @@ static int __domain_mapping(struct > dmar_domain *domain, unsigned long iov_pfn, > > dma_pte_free_pagetable(domain, > iov_pfn, end_pfn, > > > largepage_lvl + 1); > > } else { > > - pteval &= > ~(uint64_t)DMA_PTE_LARGE_PAGE; > > + pteval &= ~large_page; > > } > > > > } > > @@ -5377,7 +5398,7 @@ static int > prepare_domain_attach_device(struct iommu_domain *domain, > > pte = dmar_domain->pgd; > > if (dma_pte_present(pte)) { > > dmar_domain->pgd = (struct dma_pte *) > > - phys_to_virt(dma_pte_addr(pte)); > > + phys_to_virt(dma_pte_addr(pte, > dmar_domain)); > > free_pgtable_page(pte); > > } > > dmar_domain->agaw--; > > @@ -5386,6 +5407,46 @@ static int > prepare_domain_attach_device(struct iommu_domain *domain, > > return 0; > > } > > > > +static int intel_iommu_domain_set_attr(struct iommu_domain *domain, > > + enum iommu_attr attr, void > *data) > > +{ > > + struct dmar_domain *dmar_domain = to_dmar_domain(domain); > > + int ret = 0; > > + > > + switch (attr) { > > + case DOMAIN_ATTR_A45_HUGE_PAGE: { > > + bool *huge_page = data; > > + > > + domain_type_set_a45_huge_page(dmar_domain, *huge_page); > > + break; > > + } > > + default: > > + return -EINVAL; > > + } > > + > > + return ret; > > +} > > + > > +static int intel_iommu_domain_get_attr(struct iommu_domain *domain, > > + enum iommu_attr attr, void > *data) > > +{ > > + struct dmar_domain *dmar_domain = to_dmar_domain(domain); > > + int ret = 0; > > + > > + switch (attr) { > > + case DOMAIN_ATTR_A45_HUGE_PAGE: { > > + bool *huge_page = data; > > + > > + *huge_page = > domain_type_get_a45_huge_page(dmar_domain); > > + break; > > + } > > + default: > > + return -EINVAL; > > + } > > + > > + return ret; > > +} > > + > > static int intel_iommu_attach_device(struct iommu_domain *domain, > > struct device *dev) > > { > > @@ -5535,7 +5596,7 @@ static phys_addr_t > intel_iommu_iova_to_phys(struct iommu_domain *domain, > > > > pte = pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT, > &level); > > if (pte) > > - phys = dma_pte_addr(pte); > > + phys = dma_pte_addr(pte, dmar_domain); > > > > return phys; > > } > > @@ -5958,6 +6019,8 @@ const struct iommu_ops intel_iommu_ops = { > > .capable = intel_iommu_capable, > > .domain_alloc = intel_iommu_domain_alloc, > > .domain_free = intel_iommu_domain_free, > > + .domain_set_attr = intel_iommu_domain_set_attr, > > + .domain_get_attr = intel_iommu_domain_get_attr, > > .attach_dev = intel_iommu_attach_device, > > .detach_dev = intel_iommu_detach_device, > > .aux_attach_dev = intel_iommu_aux_attach_device, > > diff --git a/drivers/iommu/intel-pasid.c > b/drivers/iommu/intel-pasid.c > > index 040a445be300..ca7bf35cb4a0 100644 > > --- a/drivers/iommu/intel-pasid.c > > +++ b/drivers/iommu/intel-pasid.c > > @@ -553,7 +553,7 @@ int intel_pasid_setup_second_level(struct > intel_iommu *iommu, > > */ > > pgd = domain->pgd; > > for (agaw = domain->agaw; agaw > iommu->agaw; agaw--) { > > - pgd = phys_to_virt(dma_pte_addr(pgd)); > > + pgd = phys_to_virt(dma_pte_addr(pgd, domain)); > > if (!dma_pte_present(pgd)) { > > dev_err(dev, "Invalid domain page table\n"); > > return -EINVAL; > > diff --git a/include/linux/intel-iommu.h > b/include/linux/intel-iommu.h > > index ed11ef594378..4c18fdf8bca3 100644 > > --- a/include/linux/intel-iommu.h > > +++ b/include/linux/intel-iommu.h > > @@ -37,6 +37,17 @@ > > #define DMA_PTE_READ (1) > > #define DMA_PTE_WRITE (2) > > #define DMA_PTE_LARGE_PAGE (1 << 7) > > +/* > > + * PCIe Address Translation Service (ATS) allows a PCIe device > to look up VA->PA > > + * translations maintained by the IOMMU and cache them. > Unfortunately, up to at > > + * least Intel Skylake, the IOMMU fragments all ATS Translation > Responses to 4 > > + * KiB, even if the underlying page size is 2 MiB. In order to > know if a page is > > + * mapped as 2 MiB, a side-channel is defined here by setting the > > + * DMA_PTE_A45_HUGE_PAGE bit in all huge-page PTEs. This bit can > be received as > > + * part of the ATS translation response and interpreted only as > 2 MiB page size > > + * indicator, but ignored otherwise. > > + */ > > +#define DMA_PTE_A45_HUGE_PAGE (1UL << 45) > > #define DMA_PTE_SNP (1 << 11) > > > > #define CONTEXT_TT_MULTI_LEVEL 0 > > @@ -604,16 +615,6 @@ static inline void dma_clear_pte(struct > dma_pte *pte) > > pte->val = 0; > > } > > > > -static inline u64 dma_pte_addr(struct dma_pte *pte) > > -{ > > -#ifdef CONFIG_64BIT > > - return pte->val & VTD_PAGE_MASK; > > -#else > > - /* Must have a full atomic 64-bit read */ > > - return __cmpxchg64(&pte->val, 0ULL, 0ULL) & VTD_PAGE_MASK; > > -#endif > > -} > > - > > static inline bool dma_pte_present(struct dma_pte *pte) > > { > > return (pte->val & 3) != 0; > > @@ -624,6 +625,22 @@ static inline bool dma_pte_superpage(struct > dma_pte *pte) > > return (pte->val & DMA_PTE_LARGE_PAGE); > > } > > > > +bool domain_type_get_a45_huge_page(struct dmar_domain *domain); > > +static inline u64 dma_pte_addr(struct dma_pte *pte, struct > dmar_domain *domain) > > +{ > > +#ifdef CONFIG_64BIT > > + u64 mask = VTD_PAGE_MASK; > > + > > + if (dma_pte_superpage(pte) && > domain_type_get_a45_huge_page(domain)) > > + mask &= ~DMA_PTE_A45_HUGE_PAGE; > > + > > + return pte->val & mask; > > +#else > > + /* Must have a full atomic 64-bit read */ > > + return __cmpxchg64(&pte->val, 0ULL, 0ULL) & VTD_PAGE_MASK; > > +#endif > > +} > > + > > static inline int first_pte_in_page(struct dma_pte *pte) > > { > > return !((unsigned long)pte & ~VTD_PAGE_MASK); > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > > index e28e80dea141..e4231f1759a0 100644 > > --- a/include/linux/iommu.h > > +++ b/include/linux/iommu.h > > @@ -126,6 +126,7 @@ enum iommu_attr { > > DOMAIN_ATTR_FSL_PAMUV1, > > DOMAIN_ATTR_NESTING, /* two stages of translation */ > > DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, > > + DOMAIN_ATTR_A45_HUGE_PAGE, /* huge-page side channel */ > > DOMAIN_ATTR_MAX, > > }; > > > > >
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