diff options
Diffstat (limited to 'arch/x86/kvm/mmu/tdp_iter.c')
| -rw-r--r-- | arch/x86/kvm/mmu/tdp_iter.c | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c new file mode 100644 index 000000000000..ad2184cb054c --- /dev/null +++ b/arch/x86/kvm/mmu/tdp_iter.c @@ -0,0 +1,177 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include "mmu_internal.h" +#include "tdp_iter.h" +#include "spte.h" + +/* + * Recalculates the pointer to the SPTE for the current GFN and level and + * reread the SPTE. + */ +static void tdp_iter_refresh_sptep(struct tdp_iter *iter) +{ + iter->sptep = iter->pt_path[iter->level - 1] + + SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level); + iter->old_spte = READ_ONCE(*iter->sptep); +} + +static gfn_t round_gfn_for_level(gfn_t gfn, int level) +{ + return gfn & -KVM_PAGES_PER_HPAGE(level); +} + +/* + * Sets a TDP iterator to walk a pre-order traversal of the paging structure + * rooted at root_pt, starting with the walk to translate goal_gfn. + */ +void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level, + int min_level, gfn_t goal_gfn) +{ + WARN_ON(root_level < 1); + WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); + + iter->goal_gfn = goal_gfn; + iter->root_level = root_level; + iter->min_level = min_level; + iter->level = root_level; + iter->pt_path[iter->level - 1] = root_pt; + + iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level); + tdp_iter_refresh_sptep(iter); + + iter->valid = true; +} + +/* + * Given an SPTE and its level, returns a pointer containing the host virtual + * address of the child page table referenced by the SPTE. Returns null if + * there is no such entry. + */ +u64 *spte_to_child_pt(u64 spte, int level) +{ + /* + * There's no child entry if this entry isn't present or is a + * last-level entry. + */ + if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) + return NULL; + + return __va(spte_to_pfn(spte) << PAGE_SHIFT); +} + +/* + * Steps down one level in the paging structure towards the goal GFN. Returns + * true if the iterator was able to step down a level, false otherwise. + */ +static bool try_step_down(struct tdp_iter *iter) +{ + u64 *child_pt; + + if (iter->level == iter->min_level) + return false; + + /* + * Reread the SPTE before stepping down to avoid traversing into page + * tables that are no longer linked from this entry. + */ + iter->old_spte = READ_ONCE(*iter->sptep); + + child_pt = spte_to_child_pt(iter->old_spte, iter->level); + if (!child_pt) + return false; + + iter->level--; + iter->pt_path[iter->level - 1] = child_pt; + iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level); + tdp_iter_refresh_sptep(iter); + + return true; +} + +/* + * Steps to the next entry in the current page table, at the current page table + * level. The next entry could point to a page backing guest memory or another + * page table, or it could be non-present. Returns true if the iterator was + * able to step to the next entry in the page table, false if the iterator was + * already at the end of the current page table. + */ +static bool try_step_side(struct tdp_iter *iter) +{ + /* + * Check if the iterator is already at the end of the current page + * table. + */ + if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) == + (PT64_ENT_PER_PAGE - 1)) + return false; + + iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); + iter->goal_gfn = iter->gfn; + iter->sptep++; + iter->old_spte = READ_ONCE(*iter->sptep); + + return true; +} + +/* + * Tries to traverse back up a level in the paging structure so that the walk + * can continue from the next entry in the parent page table. Returns true on a + * successful step up, false if already in the root page. + */ +static bool try_step_up(struct tdp_iter *iter) +{ + if (iter->level == iter->root_level) + return false; + + iter->level++; + iter->gfn = round_gfn_for_level(iter->gfn, iter->level); + tdp_iter_refresh_sptep(iter); + + return true; +} + +/* + * Step to the next SPTE in a pre-order traversal of the paging structure. + * To get to the next SPTE, the iterator either steps down towards the goal + * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a + * highter GFN. + * + * The basic algorithm is as follows: + * 1. If the current SPTE is a non-last-level SPTE, step down into the page + * table it points to. + * 2. If the iterator cannot step down, it will try to step to the next SPTE + * in the current page of the paging structure. + * 3. If the iterator cannot step to the next entry in the current page, it will + * try to step up to the parent paging structure page. In this case, that + * SPTE will have already been visited, and so the iterator must also step + * to the side again. + */ +void tdp_iter_next(struct tdp_iter *iter) +{ + if (try_step_down(iter)) + return; + + do { + if (try_step_side(iter)) + return; + } while (try_step_up(iter)); + iter->valid = false; +} + +/* + * Restart the walk over the paging structure from the root, starting from the + * highest gfn the iterator had previously reached. Assumes that the entire + * paging structure, except the root page, may have been completely torn down + * and rebuilt. + */ +void tdp_iter_refresh_walk(struct tdp_iter *iter) +{ + gfn_t goal_gfn = iter->goal_gfn; + + if (iter->gfn > goal_gfn) + goal_gfn = iter->gfn; + + tdp_iter_start(iter, iter->pt_path[iter->root_level - 1], + iter->root_level, iter->min_level, goal_gfn); +} + |