From e9dc33b99f7acc8566f3552b85f5e91a198b9e15 Mon Sep 17 00:00:00 2001 From: "Alexander M. Merritt" Date: Tue, 19 May 2026 13:42:07 -0500 Subject: [PATCH] xen: patch to batch pvh/dom0 mem mapping Signed-off-by: Alexander M. Merritt --- config.yaml | 2 + ...001-xen-xlate_mmu-batch-gfn-mappings.patch | 271 ++++++++++++++++++ 2 files changed, 273 insertions(+) create mode 100644 patches/0001-xen-xlate_mmu-batch-gfn-mappings.patch diff --git a/config.yaml b/config.yaml index 54b493b..d626f78 100644 --- a/config.yaml +++ b/config.yaml @@ -91,6 +91,8 @@ patches: lower: '6.17' - patch: 0003-x86-amd_node-fix-null-pointer-dereference-if-amd_smn.patch lower: '6.17' +- patch: 0001-xen-xlate_mmu-batch-gfn-mappings.patch + lower: '6.6' images: - target: kernelsrc name: kernel-src diff --git a/patches/0001-xen-xlate_mmu-batch-gfn-mappings.patch b/patches/0001-xen-xlate_mmu-batch-gfn-mappings.patch new file mode 100644 index 0000000..feb5f7b --- /dev/null +++ b/patches/0001-xen-xlate_mmu-batch-gfn-mappings.patch @@ -0,0 +1,271 @@ +From 5447a754e653b94219d17f54d5bc81b0a5b41517 Mon Sep 17 00:00:00 2001 +Message-ID: <5447a754e653b94219d17f54d5bc81b0a5b41517.1779215254.git.alexander@edera.dev> +From: "Alexander M. Merritt" +Date: Tue, 19 May 2026 13:21:21 -0500 +Subject: [PATCH] xen: xlate_mmu: batch gfn mappings + +PVH dom0 wanting to map in guest memory would iterate over each page +individually invoking hypercall add_to_physmap_range, leading to high +mapping latencies. + +Refactor xen_xlate_remap_gfn_array to separately batch GFN mappings to +xen to amortize hypercall overhead. + +Signed-off-by: Alexander M. Merritt +--- + drivers/xen/xlate_mmu.c | 208 +++++++++++++++++++--------------------- + 1 file changed, 97 insertions(+), 111 deletions(-) + +diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c +index f17c4c03db30..7514e05e4420 100644 +--- a/drivers/xen/xlate_mmu.c ++++ b/drivers/xen/xlate_mmu.c +@@ -42,8 +42,29 @@ + #include + #include + ++#define XLATE_BATCH_SIZE 16 ++ + typedef void (*xen_gfn_fn_t)(unsigned long gfn, void *data); + ++struct remap_pfn { ++ struct mm_struct *mm; ++ struct page **pages; ++ pgprot_t prot; ++ unsigned long i; ++}; ++ ++static int remap_pfn_fn(pte_t *ptep, unsigned long addr, void *data) ++{ ++ struct remap_pfn *r = data; ++ struct page *page = r->pages[r->i]; ++ pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), r->prot)); ++ ++ set_pte_at(r->mm, addr, ptep, pte); ++ r->i++; ++ ++ return 0; ++} ++ + /* Break down the pages in 4KB chunk and call fn for each gfn */ + static void xen_for_each_gfn(struct page **pages, unsigned nr_gfn, + xen_gfn_fn_t fn, void *data) +@@ -61,113 +82,97 @@ static void xen_for_each_gfn(struct page **pages, unsigned nr_gfn, + } + } + +-struct remap_data { +- xen_pfn_t *fgfn; /* foreign domain's gfn */ +- int nr_fgfn; /* Number of foreign gfn left to map */ +- pgprot_t prot; +- domid_t domid; +- struct vm_area_struct *vma; +- int index; +- struct page **pages; +- struct xen_remap_gfn_info *info; +- int *err_ptr; +- int mapped; +- +- /* Hypercall parameters */ +- int h_errs[XEN_PFN_PER_PAGE]; +- xen_ulong_t h_idxs[XEN_PFN_PER_PAGE]; +- xen_pfn_t h_gpfns[XEN_PFN_PER_PAGE]; +- +- int h_iter; /* Iterator */ +-}; +- +-static void setup_hparams(unsigned long gfn, void *data) ++int xen_xlate_remap_gfn_array(struct vm_area_struct *vma, unsigned long addr, ++ xen_pfn_t *gfn, int nr, int *err_ptr, ++ pgprot_t prot, unsigned domid, ++ struct page **pages) + { +- struct remap_data *info = data; ++ /* Source GFNs in foreign domain P2M (combined with XENMAPSPACE_gmfn_foreign) */ ++ xen_ulong_t h_idxs[XLATE_BATCH_SIZE]; + +- info->h_idxs[info->h_iter] = *info->fgfn; +- info->h_gpfns[info->h_iter] = gfn; +- info->h_errs[info->h_iter] = 0; ++ /* Destination GFNs in dom0's P2M. Extracted from pages[] */ ++ xen_pfn_t h_gpfns[XLATE_BATCH_SIZE]; + +- info->h_iter++; +- info->fgfn++; +-} ++ /* h_idxs and h_gpfns exist as pairs: we map into dom0's GFN the same MFN for the GFN in foreign domain. */ + +-static int remap_pte_fn(pte_t *ptep, unsigned long addr, void *data) +-{ +- struct remap_data *info = data; +- struct page *page = info->pages[info->index++]; +- pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), info->prot)); +- int rc, nr_gfn; +- uint32_t i; +- struct xen_add_to_physmap_range xatp = { +- .domid = DOMID_SELF, +- .foreign_domid = info->domid, +- .space = XENMAPSPACE_gmfn_foreign, +- }; ++ int h_errs[XLATE_BATCH_SIZE]; ++ int mapped = 0; ++ int gfn_off = 0; /* index into gfn/err */ ++ int page_off = 0; /* index into pages */ + +- nr_gfn = min_t(typeof(info->nr_fgfn), XEN_PFN_PER_PAGE, info->nr_fgfn); +- info->nr_fgfn -= nr_gfn; ++ BUILD_BUG_ON(XLATE_BATCH_SIZE % XEN_PFN_PER_PAGE != 0); ++ BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO))); + +- info->h_iter = 0; +- xen_for_each_gfn(&page, nr_gfn, setup_hparams, info); +- BUG_ON(info->h_iter != nr_gfn); ++ while (nr > 0) { ++ int rc, i; + +- set_xen_guest_handle(xatp.idxs, info->h_idxs); +- set_xen_guest_handle(xatp.gpfns, info->h_gpfns); +- set_xen_guest_handle(xatp.errs, info->h_errs); +- xatp.size = nr_gfn; ++ int batch = min(XLATE_BATCH_SIZE, nr); /* xen GFN units */ + +- rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp); ++ /* arm: page size may be larger than xen */ ++ int batch_pages = DIV_ROUND_UP(batch, XEN_PFN_PER_PAGE); ++ unsigned long batch_range = (unsigned long)batch_pages ++ << PAGE_SHIFT; + +- /* info->err_ptr expect to have one error status per Xen PFN */ +- for (i = 0; i < nr_gfn; i++) { +- int err = (rc < 0) ? rc : info->h_errs[i]; ++ /* set up arguments to hypercall to edit dom0 P2M */ + +- *(info->err_ptr++) = err; +- if (!err) +- info->mapped++; +- } ++ unsigned long xen_pfn = 0; + +- /* +- * Note: The hypercall will return 0 in most of the case if even if +- * all the fgmfn are not mapped. We still have to update the pte +- * as the userspace may decide to continue. +- */ +- if (!rc) +- set_pte_at(info->vma->vm_mm, addr, ptep, pte); ++ /* for each _source_ page in the batch (arm: pages may be larger than 4Ki) */ ++ for (i = 0; i < batch; i++) { ++ if ((i % XEN_PFN_PER_PAGE) == 0) { ++ xen_pfn = page_to_xen_pfn( ++ pages[page_off + i / XEN_PFN_PER_PAGE]); ++ } ++ h_idxs[i] = gfn[gfn_off + i]; ++ h_gpfns[i] = pfn_to_gfn(xen_pfn++); ++ h_errs[i] = 0; ++ } + +- return 0; +-} ++ struct xen_add_to_physmap_range xatp = { ++ .domid = DOMID_SELF, ++ .foreign_domid = domid, ++ .space = XENMAPSPACE_gmfn_foreign, ++ .size = batch, ++ }; ++ ++ set_xen_guest_handle(xatp.idxs, h_idxs); ++ set_xen_guest_handle(xatp.gpfns, h_gpfns); ++ set_xen_guest_handle(xatp.errs, h_errs); ++ ++ rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp); ++ ++ if (rc == 0) { ++ struct remap_pfn r = { ++ .mm = vma->vm_mm, ++ .pages = &pages[page_off], ++ .prot = prot, ++ .i = 0, ++ }; ++ int err = apply_to_page_range(vma->vm_mm, addr, ++ batch_range, remap_pfn_fn, ++ &r); ++ if (err < 0) { ++ for (i = 0; i < batch; i++) ++ err_ptr[gfn_off + i] = err; ++ return err; ++ } ++ } + +-int xen_xlate_remap_gfn_array(struct vm_area_struct *vma, +- unsigned long addr, +- xen_pfn_t *gfn, int nr, +- int *err_ptr, pgprot_t prot, +- unsigned domid, +- struct page **pages) +-{ +- int err; +- struct remap_data data; +- unsigned long range = DIV_ROUND_UP(nr, XEN_PFN_PER_PAGE) << PAGE_SHIFT; ++ for (i = 0; i < batch; i++) { ++ int err = (rc < 0) ? rc : h_errs[i]; ++ err_ptr[gfn_off + i] = err; ++ if (!err) ++ mapped++; ++ } + +- /* Kept here for the purpose of making sure code doesn't break +- x86 PVOPS */ +- BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO))); ++ addr += batch_range; ++ gfn_off += batch; ++ page_off += batch_pages; ++ nr -= batch; ++ cond_resched(); ++ } + +- data.fgfn = gfn; +- data.nr_fgfn = nr; +- data.prot = prot; +- data.domid = domid; +- data.vma = vma; +- data.pages = pages; +- data.index = 0; +- data.err_ptr = err_ptr; +- data.mapped = 0; +- +- err = apply_to_page_range(vma->vm_mm, addr, range, +- remap_pte_fn, &data); +- return err < 0 ? err : data.mapped; ++ return mapped; + } + EXPORT_SYMBOL_GPL(xen_xlate_remap_gfn_array); + +@@ -262,25 +267,6 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt, + return 0; + } + +-struct remap_pfn { +- struct mm_struct *mm; +- struct page **pages; +- pgprot_t prot; +- unsigned long i; +-}; +- +-static int remap_pfn_fn(pte_t *ptep, unsigned long addr, void *data) +-{ +- struct remap_pfn *r = data; +- struct page *page = r->pages[r->i]; +- pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), r->prot)); +- +- set_pte_at(r->mm, addr, ptep, pte); +- r->i++; +- +- return 0; +-} +- + /* Used by the privcmd module, but has to be built-in on ARM */ + int xen_remap_vma_range(struct vm_area_struct *vma, unsigned long addr, unsigned long len) + { +-- +2.48.1 +