|
| 1 | +From 0b3410862d1c9a6be6973314f6979cf309b13e13 Mon Sep 17 00:00:00 2001 |
| 2 | +Message-ID: <0b3410862d1c9a6be6973314f6979cf309b13e13.1779978695.git.alexander@edera.dev> |
| 3 | +In-Reply-To: <5bc298c60601161ec0f012d38e4cc021347b9831.1779978695.git.alexander@edera.dev> |
| 4 | +References: <5bc298c60601161ec0f012d38e4cc021347b9831.1779978695.git.alexander@edera.dev> |
| 5 | +From: "Alexander M. Merritt" <alexander@edera.dev> |
| 6 | +Date: Wed, 27 May 2026 13:47:13 -0500 |
| 7 | +Subject: [PATCH 2/2] xen: xlate_mmu: batch gfn mappings |
| 8 | + |
| 9 | +PVH dom0 wanting to map in guest memory would iterate over each page |
| 10 | +individually invoking hypercall add_to_physmap_range, leading to high |
| 11 | +mapping latencies. |
| 12 | + |
| 13 | +Refactor xen_xlate_remap_gfn_array to separately batch GFN mappings to |
| 14 | +the hypervisor to amortize hypercall overhead. |
| 15 | + |
| 16 | +Signed-off-by: Alexander M. Merritt <alexander@edera.dev> |
| 17 | +--- |
| 18 | + drivers/xen/xlate_mmu.c | 133 +++++++++++++++++++++++----------------- |
| 19 | + 1 file changed, 76 insertions(+), 57 deletions(-) |
| 20 | + |
| 21 | +diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c |
| 22 | +index 6a15396b08aa..f8dd332b7f46 100644 |
| 23 | +--- a/drivers/xen/xlate_mmu.c |
| 24 | ++++ b/drivers/xen/xlate_mmu.c |
| 25 | +@@ -42,6 +42,9 @@ |
| 26 | + #include <xen/interface/memory.h> |
| 27 | + #include <xen/balloon.h> |
| 28 | + |
| 29 | ++/* Issue up to this many GFN mapping requests in a batch at a time. */ |
| 30 | ++#define XLATE_BATCH_SIZE 16 |
| 31 | ++ |
| 32 | + typedef void (*xen_gfn_fn_t)(unsigned long gfn, void *data); |
| 33 | + |
| 34 | + /* Break down the pages in 4KB chunk and call fn for each gfn */ |
| 35 | +@@ -92,12 +95,19 @@ struct remap_data { |
| 36 | + int *err_ptr; |
| 37 | + int mapped; |
| 38 | + |
| 39 | +- /* Hypercall parameters */ |
| 40 | +- int h_errs[XEN_PFN_PER_PAGE]; |
| 41 | +- xen_ulong_t h_idxs[XEN_PFN_PER_PAGE]; |
| 42 | +- xen_pfn_t h_gpfns[XEN_PFN_PER_PAGE]; |
| 43 | ++ /* Hypercall parameters. |
| 44 | ++ * |
| 45 | ++ * idxs: source GFNs in foreign domain P2M (combined with XENMAPSPACE_gmfn_foreign) |
| 46 | ++ * gpfns: destination GFNs in dom0's P2M. Extracted from pages[] |
| 47 | ++ * |
| 48 | ++ * h_idxs and h_gpfns exist as pairs: we map into dom0's GFN |
| 49 | ++ * the same MFN for the GFN in the foreign domain. |
| 50 | ++ */ |
| 51 | ++ int h_errs[XLATE_BATCH_SIZE]; |
| 52 | ++ xen_ulong_t h_idxs[XLATE_BATCH_SIZE]; |
| 53 | ++ xen_pfn_t h_gpfns[XLATE_BATCH_SIZE]; |
| 54 | + |
| 55 | +- int h_iter; /* Iterator */ |
| 56 | ++ int h_iter; |
| 57 | + }; |
| 58 | + |
| 59 | + static void setup_hparams(unsigned long gfn, void *data) |
| 60 | +@@ -112,53 +122,6 @@ static void setup_hparams(unsigned long gfn, void *data) |
| 61 | + info->fgfn++; |
| 62 | + } |
| 63 | + |
| 64 | +-static int remap_pte_fn(pte_t *ptep, unsigned long addr, void *data) |
| 65 | +-{ |
| 66 | +- struct remap_data *info = data; |
| 67 | +- struct page *page = info->pages[info->index++]; |
| 68 | +- pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), info->prot)); |
| 69 | +- int rc, nr_gfn; |
| 70 | +- uint32_t i; |
| 71 | +- struct xen_add_to_physmap_range xatp = { |
| 72 | +- .domid = DOMID_SELF, |
| 73 | +- .foreign_domid = info->domid, |
| 74 | +- .space = XENMAPSPACE_gmfn_foreign, |
| 75 | +- }; |
| 76 | +- |
| 77 | +- nr_gfn = min_t(typeof(info->nr_fgfn), XEN_PFN_PER_PAGE, info->nr_fgfn); |
| 78 | +- info->nr_fgfn -= nr_gfn; |
| 79 | +- |
| 80 | +- info->h_iter = 0; |
| 81 | +- xen_for_each_gfn(&page, nr_gfn, setup_hparams, info); |
| 82 | +- BUG_ON(info->h_iter != nr_gfn); |
| 83 | +- |
| 84 | +- set_xen_guest_handle(xatp.idxs, info->h_idxs); |
| 85 | +- set_xen_guest_handle(xatp.gpfns, info->h_gpfns); |
| 86 | +- set_xen_guest_handle(xatp.errs, info->h_errs); |
| 87 | +- xatp.size = nr_gfn; |
| 88 | +- |
| 89 | +- rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp); |
| 90 | +- |
| 91 | +- /* info->err_ptr expect to have one error status per Xen PFN */ |
| 92 | +- for (i = 0; i < nr_gfn; i++) { |
| 93 | +- int err = (rc < 0) ? rc : info->h_errs[i]; |
| 94 | +- |
| 95 | +- *(info->err_ptr++) = err; |
| 96 | +- if (!err) |
| 97 | +- info->mapped++; |
| 98 | +- } |
| 99 | +- |
| 100 | +- /* |
| 101 | +- * Note: The hypercall will return 0 in most of the case if even if |
| 102 | +- * all the fgmfn are not mapped. We still have to update the pte |
| 103 | +- * as the userspace may decide to continue. |
| 104 | +- */ |
| 105 | +- if (!rc) |
| 106 | +- set_pte_at(info->vma->vm_mm, addr, ptep, pte); |
| 107 | +- |
| 108 | +- return 0; |
| 109 | +-} |
| 110 | +- |
| 111 | + int xen_xlate_remap_gfn_array(struct vm_area_struct *vma, |
| 112 | + unsigned long addr, |
| 113 | + xen_pfn_t *gfn, int nr, |
| 114 | +@@ -166,9 +129,10 @@ int xen_xlate_remap_gfn_array(struct vm_area_struct *vma, |
| 115 | + unsigned domid, |
| 116 | + struct page **pages) |
| 117 | + { |
| 118 | +- int err; |
| 119 | + struct remap_data data; |
| 120 | +- unsigned long range = DIV_ROUND_UP(nr, XEN_PFN_PER_PAGE) << PAGE_SHIFT; |
| 121 | ++ int page_off = 0; |
| 122 | ++ |
| 123 | ++ BUILD_BUG_ON(XLATE_BATCH_SIZE % XEN_PFN_PER_PAGE != 0); |
| 124 | + |
| 125 | + /* Kept here for the purpose of making sure code doesn't break |
| 126 | + x86 PVOPS */ |
| 127 | +@@ -184,9 +148,64 @@ int xen_xlate_remap_gfn_array(struct vm_area_struct *vma, |
| 128 | + data.err_ptr = err_ptr; |
| 129 | + data.mapped = 0; |
| 130 | + |
| 131 | +- err = apply_to_page_range(vma->vm_mm, addr, range, |
| 132 | +- remap_pte_fn, &data); |
| 133 | +- return err < 0 ? err : data.mapped; |
| 134 | ++ while (data.nr_fgfn > 0) { |
| 135 | ++ int batch = min_t(int, XLATE_BATCH_SIZE, data.nr_fgfn); /* xen GFN units */ |
| 136 | ++ /* NOTE: on ARM, page size may be larger than in Xen */ |
| 137 | ++ int batch_pages = DIV_ROUND_UP(batch, XEN_PFN_PER_PAGE); |
| 138 | ++ unsigned long batch_range = (unsigned long)batch_pages << PAGE_SHIFT; |
| 139 | ++ |
| 140 | ++ struct xen_add_to_physmap_range xatp = { |
| 141 | ++ .domid = DOMID_SELF, |
| 142 | ++ .foreign_domid = domid, |
| 143 | ++ .space = XENMAPSPACE_gmfn_foreign, |
| 144 | ++ .size = batch, |
| 145 | ++ }; |
| 146 | ++ |
| 147 | ++ int rc, i; |
| 148 | ++ |
| 149 | ++ data.h_iter = 0; |
| 150 | ++ xen_for_each_gfn(&pages[page_off], batch, setup_hparams, &data); |
| 151 | ++ data.nr_fgfn -= batch; |
| 152 | ++ |
| 153 | ++ set_xen_guest_handle(xatp.idxs, data.h_idxs); |
| 154 | ++ set_xen_guest_handle(xatp.gpfns, data.h_gpfns); |
| 155 | ++ set_xen_guest_handle(xatp.errs, data.h_errs); |
| 156 | ++ |
| 157 | ++ rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp); |
| 158 | ++ |
| 159 | ++ /* |
| 160 | ++ * Note: The hypercall will return 0 in most of the case if even if |
| 161 | ++ * all the fgmfn are not mapped. We still have to update the pte |
| 162 | ++ * as the userspace may decide to continue. |
| 163 | ++ */ |
| 164 | ++ if (rc == 0) { |
| 165 | ++ struct remap_pfn r = { |
| 166 | ++ .mm = vma->vm_mm, |
| 167 | ++ .pages = &pages[page_off], |
| 168 | ++ .prot = prot, |
| 169 | ++ .i = 0, |
| 170 | ++ }; |
| 171 | ++ int walk_err = apply_to_page_range(vma->vm_mm, addr, |
| 172 | ++ batch_range, |
| 173 | ++ remap_pfn_fn, &r); |
| 174 | ++ if (walk_err < 0) |
| 175 | ++ return walk_err; |
| 176 | ++ } |
| 177 | ++ |
| 178 | ++ /* err_ptr expected to have one error status per Xen PFN */ |
| 179 | ++ for (i = 0; i < batch; i++) { |
| 180 | ++ int err = (rc < 0) ? rc : data.h_errs[i]; |
| 181 | ++ *(data.err_ptr++) = err; |
| 182 | ++ if (!err) |
| 183 | ++ data.mapped++; |
| 184 | ++ } |
| 185 | ++ |
| 186 | ++ addr += batch_range; |
| 187 | ++ page_off += batch_pages; |
| 188 | ++ cond_resched(); |
| 189 | ++ } |
| 190 | ++ |
| 191 | ++ return data.mapped; |
| 192 | + } |
| 193 | + EXPORT_SYMBOL_GPL(xen_xlate_remap_gfn_array); |
| 194 | + |
| 195 | +-- |
| 196 | +2.48.1 |
| 197 | + |
0 commit comments