From ddcadb297ce5cc1cec0b0882d8b750e5e06fc9f4 Mon Sep 17 00:00:00 2001 From: Oliver Upton Date: Fri, 2 Dec 2022 18:51:52 +0000 Subject: [PATCH] KVM: arm64: Ignore EAGAIN for walks outside of a fault The page table walkers are invoked outside fault handling paths, such as write protecting a range of memory. EAGAIN is generally used by the walkers to retry execution due to races on a particular PTE, like taking an access fault on a PTE being invalidated from another thread. This early return behavior is undesirable for walkers that operate outside a fault handler. Suppress EAGAIN and continue the walk if operating outside a fault handler. Link: https://lore.kernel.org/r/20221202185156.696189-3-oliver.upton@linux.dev Signed-off-by: Oliver Upton --- arch/arm64/include/asm/kvm_pgtable.h | 3 +++ arch/arm64/kvm/hyp/pgtable.c | 30 +++++++++++++++++++++++++++--- arch/arm64/kvm/mmu.c | 4 +++- 3 files changed, 33 insertions(+), 4 deletions(-) diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h index 192f33b..4cd6762 100644 --- a/arch/arm64/include/asm/kvm_pgtable.h +++ b/arch/arm64/include/asm/kvm_pgtable.h @@ -193,12 +193,15 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end, * children. * @KVM_PGTABLE_WALK_SHARED: Indicates the page-tables may be shared * with other software walkers. + * @KVM_PGTABLE_WALK_HANDLE_FAULT: Indicates the page-table walk was + * invoked from a fault handler. */ enum kvm_pgtable_walk_flags { KVM_PGTABLE_WALK_LEAF = BIT(0), KVM_PGTABLE_WALK_TABLE_PRE = BIT(1), KVM_PGTABLE_WALK_TABLE_POST = BIT(2), KVM_PGTABLE_WALK_SHARED = BIT(3), + KVM_PGTABLE_WALK_HANDLE_FAULT = BIT(4), }; struct kvm_pgtable_visit_ctx { diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index b11cf2c..98818214 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -168,6 +168,25 @@ static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data, return walker->cb(ctx, visit); } +static bool kvm_pgtable_walk_continue(const struct kvm_pgtable_walker *walker, + int r) +{ + /* + * Visitor callbacks return EAGAIN when the conditions that led to a + * fault are no longer reflected in the page tables due to a race to + * update a PTE. In the context of a fault handler this is interpreted + * as a signal to retry guest execution. + * + * Ignore the return code altogether for walkers outside a fault handler + * (e.g. write protecting a range of memory) and chug along with the + * page table walk. + */ + if (r == -EAGAIN) + return !(walker->flags & KVM_PGTABLE_WALK_HANDLE_FAULT); + + return !r; +} + static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data, struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level); @@ -200,7 +219,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, table = kvm_pte_table(ctx.old, level); } - if (ret) + if (!kvm_pgtable_walk_continue(data->walker, ret)) goto out; if (!table) { @@ -211,13 +230,16 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops); ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1); - if (ret) + if (!kvm_pgtable_walk_continue(data->walker, ret)) goto out; if (ctx.flags & KVM_PGTABLE_WALK_TABLE_POST) ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_POST); out: + if (kvm_pgtable_walk_continue(data->walker, ret)) + return 0; + return ret; } @@ -1095,7 +1117,8 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr) { kvm_pte_t pte = 0; stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0, - &pte, NULL, 0); + &pte, NULL, + KVM_PGTABLE_WALK_HANDLE_FAULT); dsb(ishst); return pte; } @@ -1141,6 +1164,7 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr, clr |= KVM_PTE_LEAF_ATTR_HI_S2_XN; ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level, + KVM_PGTABLE_WALK_HANDLE_FAULT | KVM_PGTABLE_WALK_SHARED); if (!ret) kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, pgt->mmu, addr, level); diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 3ddee41..edfbe85 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1381,7 +1381,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, else ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize, __pfn_to_phys(pfn), prot, - memcache, KVM_PGTABLE_WALK_SHARED); + memcache, + KVM_PGTABLE_WALK_HANDLE_FAULT | + KVM_PGTABLE_WALK_SHARED); /* Mark the page dirty only if the fault is handled successfully */ if (writable && !ret) { -- 2.7.4