From: Oliver Upton <oliver.upton@linux.dev>
Date: Tue, 27 Jun 2023 23:54:05 +0000
Subject: [PATCH] KVM: arm64: Correctly handle page aging notifiers for
unaligned memslot
References: bsc#1012628
Patch-mainline: 6.4.7
Git-commit: df6556adf27b7372cfcd97e1c0afb0d516c8279f
commit df6556adf27b7372cfcd97e1c0afb0d516c8279f upstream.
Userspace is allowed to select any PAGE_SIZE aligned hva to back guest
memory. This is even the case with hugepages, although it is a rather
suboptimal configuration as PTE level mappings are used at stage-2.
The arm64 page aging handlers have an assumption that the specified
range is exactly one page/block of memory, which in the aforementioned
case is not necessarily true. All together this leads to the WARN() in
kvm_age_gfn() firing.
However, the WARN is only part of the issue as the table walkers visit
at most a single leaf PTE. For hugepage-backed memory in a memslot that
isn't hugepage-aligned, page aging entirely misses accesses to the
hugepage beyond the first page in the memslot.
Add a new walker dedicated to handling page aging MMU notifiers capable
of walking a range of PTEs. Convert kvm(_test)_age_gfn() over to the new
walker and drop the WARN that caught the issue in the first place. The
implementation of this walker was inspired by the test_clear_young()
implementation by Yu Zhao [*], but repurposed to address a bug in the
existing aging implementation.
Cc: stable@vger.kernel.org # v5.15
Fixes: 056aad67f836 ("kvm: arm/arm64: Rework gpa callback handlers")
Link: https://lore.kernel.org/kvmarm/20230526234435.662652-6-yuzhao@google.com/
Co-developed-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: Reiji Watanabe <reijiw@google.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
Link: https://lore.kernel.org/r/20230627235405.4069823-1-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
arch/arm64/include/asm/kvm_pgtable.h | 26 ++++++---------
arch/arm64/kvm/hyp/pgtable.c | 47 ++++++++++++++++++++++------
arch/arm64/kvm/mmu.c | 18 +++++------
3 files changed, 55 insertions(+), 36 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 93bd0975..f5e5730c 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -556,22 +556,26 @@ int kvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size);
kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr);
/**
- * kvm_pgtable_stage2_mkold() - Clear the access flag in a page-table entry.
+ * kvm_pgtable_stage2_test_clear_young() - Test and optionally clear the access
+ * flag in a page-table entry.
* @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*().
* @addr: Intermediate physical address to identify the page-table entry.
+ * @size: Size of the address range to visit.
+ * @mkold: True if the access flag should be cleared.
*
* The offset of @addr within a page is ignored.
*
- * If there is a valid, leaf page-table entry used to translate @addr, then
- * clear the access flag in that entry.
+ * Tests and conditionally clears the access flag for every valid, leaf
+ * page-table entry used to translate the range [@addr, @addr + @size).
*
* Note that it is the caller's responsibility to invalidate the TLB after
* calling this function to ensure that the updated permissions are visible
* to the CPUs.
*
- * Return: The old page-table entry prior to clearing the flag, 0 on failure.
+ * Return: True if any of the visited PTEs had the access flag set.
*/
-kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr);
+bool kvm_pgtable_stage2_test_clear_young(struct kvm_pgtable *pgt, u64 addr,
+ u64 size, bool mkold);
/**
* kvm_pgtable_stage2_relax_perms() - Relax the permissions enforced by a
@@ -593,18 +597,6 @@ kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr);
int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
enum kvm_pgtable_prot prot);
-/**
- * kvm_pgtable_stage2_is_young() - Test whether a page-table entry has the
- * access flag set.
- * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*().
- * @addr: Intermediate physical address to identify the page-table entry.
- *
- * The offset of @addr within a page is ignored.
- *
- * Return: True if the page-table entry has the access flag set, false otherwise.
- */
-bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr);
-
/**
* kvm_pgtable_stage2_flush_range() - Clean and invalidate data cache to Point
* of Coherency for guest stage-2 address
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 37bd64e9..14fd3c58 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1173,25 +1173,54 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
return pte;
}
-kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr)
+struct stage2_age_data {
+ bool mkold;
+ bool young;
+};
+
+static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx,
+ enum kvm_pgtable_walk_flags visit)
{
- kvm_pte_t pte = 0;
- stage2_update_leaf_attrs(pgt, addr, 1, 0, KVM_PTE_LEAF_ATTR_LO_S2_AF,
- &pte, NULL, 0);
+ kvm_pte_t new = ctx->old & ~KVM_PTE_LEAF_ATTR_LO_S2_AF;
+ struct stage2_age_data *data = ctx->arg;
+
+ if (!kvm_pte_valid(ctx->old) || new == ctx->old)
+ return 0;
+
+ data->young = true;
+
+ /*
+ * stage2_age_walker() is always called while holding the MMU lock for
+ * write, so this will always succeed. Nonetheless, this deliberately
+ * follows the race detection pattern of the other stage-2 walkers in
+ * case the locking mechanics of the MMU notifiers is ever changed.
+ */
+ if (data->mkold && !stage2_try_set_pte(ctx, new))
+ return -EAGAIN;
+
/*
* "But where's the TLBI?!", you scream.
* "Over in the core code", I sigh.
*
* See the '->clear_flush_young()' callback on the KVM mmu notifier.
*/
- return pte;
+ return 0;
}
-bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr)
+bool kvm_pgtable_stage2_test_clear_young(struct kvm_pgtable *pgt, u64 addr,
+ u64 size, bool mkold)
{
- kvm_pte_t pte = 0;
- stage2_update_leaf_attrs(pgt, addr, 1, 0, 0, &pte, NULL, 0);
- return pte & KVM_PTE_LEAF_ATTR_LO_S2_AF;
+ struct stage2_age_data data = {
+ .mkold = mkold,
+ };
+ struct kvm_pgtable_walker walker = {
+ .cb = stage2_age_walker,
+ .arg = &data,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ };
+
+ WARN_ON(kvm_pgtable_walk(pgt, addr, size, &walker));
+ return data.young;
}
int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 3b9d4d24..8a7e9381 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1639,27 +1639,25 @@ bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
u64 size = (range->end - range->start) << PAGE_SHIFT;
- kvm_pte_t kpte;
- pte_t pte;
if (!kvm->arch.mmu.pgt)
return false;
- WARN_ON(size != PAGE_SIZE && size != PMD_SIZE && size != PUD_SIZE);
-
- kpte = kvm_pgtable_stage2_mkold(kvm->arch.mmu.pgt,
- range->start << PAGE_SHIFT);
- pte = __pte(kpte);
- return pte_valid(pte) && pte_young(pte);
+ return kvm_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
+ range->start << PAGE_SHIFT,
+ size, true);
}
bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
+ u64 size = (range->end - range->start) << PAGE_SHIFT;
+
if (!kvm->arch.mmu.pgt)
return false;
- return kvm_pgtable_stage2_is_young(kvm->arch.mmu.pgt,
- range->start << PAGE_SHIFT);
+ return kvm_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
+ range->start << PAGE_SHIFT,
+ size, false);
}
phys_addr_t kvm_mmu_get_httbr(void)
--
2.35.3