[PATCH 07/14] KVM: arm64: Enable forcing page-level stage-2 mappings

From: Quentin Perret
Date: Mon Jul 19 2021 - 06:48:16 EST

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Much of the stage-2 manipulation logic relies on being able to destroy
block mappings if e.g. installing a smaller mapping in the range. The
rationale for this behaviour is that stage-2 mappings can always be
re-created lazily. However, this gets more complicated when the stage-2
page-table is used to store metadata about the underlying pages. In such
a case, destroying a block mapping may lead to losing part of the
state, and confuse the user of those metadata (such as the hypervisor in
nVHE protected mode).

To fix this, introduce a callback function in the pgtable struct which
is called during all map operations to determine whether the mappings
can us blocks, or should be forced to page-granularity level. This is
used by the hypervisor when creating the host stage-2 to force
page-level mappings when using non-default protection attributes.

Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_pgtable.h | 63 +++++++++++++++++----------
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 16 +++++--
arch/arm64/kvm/hyp/pgtable.c | 20 +++++++--
3 files changed, 69 insertions(+), 30 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index af62203d2f7a..dd72653314c7 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -75,25 +75,6 @@ enum kvm_pgtable_stage2_flags {
KVM_PGTABLE_S2_IDMAP = BIT(1),
};

-/**
- * struct kvm_pgtable - KVM page-table.
- * @ia_bits: Maximum input address size, in bits.
- * @start_level: Level at which the page-table walk starts.
- * @pgd: Pointer to the first top-level entry of the page-table.
- * @mm_ops: Memory management callbacks.
- * @mmu: Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
- */
-struct kvm_pgtable {
- u32 ia_bits;
- u32 start_level;
- kvm_pte_t *pgd;
- struct kvm_pgtable_mm_ops *mm_ops;
-
- /* Stage-2 only */
- struct kvm_s2_mmu *mmu;
- enum kvm_pgtable_stage2_flags flags;
-};
-
/**
* enum kvm_pgtable_prot - Page-table permissions and attributes.
* @KVM_PGTABLE_PROT_X: Execute permission.
@@ -109,11 +90,41 @@ enum kvm_pgtable_prot {
KVM_PGTABLE_PROT_DEVICE = BIT(3),
};

-#define PAGE_HYP (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
+#define KVM_PGTABLE_PROT_RW (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
+#define KVM_PGTABLE_PROT_RWX (KVM_PGTABLE_PROT_RW | KVM_PGTABLE_PROT_X)
+
+#define PAGE_HYP KVM_PGTABLE_PROT_RW
#define PAGE_HYP_EXEC (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_X)
#define PAGE_HYP_RO (KVM_PGTABLE_PROT_R)
#define PAGE_HYP_DEVICE (PAGE_HYP | KVM_PGTABLE_PROT_DEVICE)

+typedef bool (*kvm_pgtable_want_pte_cb_t)(u64 addr, u64 end,
+ enum kvm_pgtable_prot prot);
+
+/**
+ * struct kvm_pgtable - KVM page-table.
+ * @ia_bits: Maximum input address size, in bits.
+ * @start_level: Level at which the page-table walk starts.
+ * @pgd: Pointer to the first top-level entry of the page-table.
+ * @mm_ops: Memory management callbacks.
+ * @mmu: Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
+ * @flags: Stage-2 page-table flags.
+ * @want_pte_cb: Callback function used during map operations to decide
+ * whether block mappings can be used to map the given IPA
+ * range.
+ */
+struct kvm_pgtable {
+ u32 ia_bits;
+ u32 start_level;
+ kvm_pte_t *pgd;
+ struct kvm_pgtable_mm_ops *mm_ops;
+
+ /* Stage-2 only */
+ struct kvm_s2_mmu *mmu;
+ enum kvm_pgtable_stage2_flags flags;
+ kvm_pgtable_want_pte_cb_t want_pte_cb;
+};
+
/**
* struct kvm_mem_range - Range of Intermediate Physical Addresses
* @start: Start of the range.
@@ -216,21 +227,25 @@ int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift);

/**
- * kvm_pgtable_stage2_init_flags() - Initialise a guest stage-2 page-table.
+ * kvm_pgtable_stage2_init_full() - Initialise a guest stage-2 page-table.
* @pgt: Uninitialised page-table structure to initialise.
* @arch: Arch-specific KVM structure representing the guest virtual
* machine.
* @mm_ops: Memory management callbacks.
* @flags: Stage-2 configuration flags.
+ * @want_pte_cb: Callback function used during map operations to decide
+ * whether block mappings can be used to map the given IPA
+ * range.
*
* Return: 0 on success, negative error code on failure.
*/
-int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch,
+int kvm_pgtable_stage2_init_full(struct kvm_pgtable *pgt, struct kvm_arch *arch,
struct kvm_pgtable_mm_ops *mm_ops,
- enum kvm_pgtable_stage2_flags flags);
+ enum kvm_pgtable_stage2_flags flags,
+ kvm_pgtable_want_pte_cb_t want_pte_cb);

#define kvm_pgtable_stage2_init(pgt, arch, mm_ops) \
- kvm_pgtable_stage2_init_flags(pgt, arch, mm_ops, 0)
+ kvm_pgtable_stage2_init_full(pgt, arch, mm_ops, 0, NULL)

/**
* kvm_pgtable_stage2_destroy() - Destroy an unused guest stage-2 page-table.
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 58edc62be6f7..cdace80d3e28 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -89,6 +89,7 @@ static void prepare_host_vtcr(void)
id_aa64mmfr1_el1_sys_val, phys_shift);
}

+static bool host_stage2_want_pte_cb(u64 addr, u64 end, enum kvm_pgtable_prot prot);
int kvm_host_prepare_stage2(void *pgt_pool_base)
{
struct kvm_s2_mmu *mmu = &host_kvm.arch.mmu;
@@ -101,8 +102,9 @@ int kvm_host_prepare_stage2(void *pgt_pool_base)
if (ret)
return ret;

- ret = kvm_pgtable_stage2_init_flags(&host_kvm.pgt, &host_kvm.arch,
- &host_kvm.mm_ops, KVM_HOST_S2_FLAGS);
+ ret = kvm_pgtable_stage2_init_full(&host_kvm.pgt, &host_kvm.arch,
+ &host_kvm.mm_ops, KVM_HOST_S2_FLAGS,
+ host_stage2_want_pte_cb);
if (ret)
return ret;

@@ -225,9 +227,17 @@ static inline int __host_stage2_idmap(u64 start, u64 end,
__ret; \
})

+static bool host_stage2_want_pte_cb(u64 addr, u64 end, enum kvm_pgtable_prot prot)
+{
+ if (range_is_memory(addr, end))
+ return prot != KVM_PGTABLE_PROT_RWX;
+ else
+ return prot != KVM_PGTABLE_PROT_RW;
+}
+
static int host_stage2_idmap(u64 addr)
{
- enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W;
+ enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_RW;
struct kvm_mem_range range;
bool is_memory = find_mem_range(addr, &range);
int ret;
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 34cf67997a82..5bdbe7a31551 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -452,6 +452,8 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
pgt->start_level = KVM_PGTABLE_MAX_LEVELS - levels;
pgt->mm_ops = mm_ops;
pgt->mmu = NULL;
+ pgt->want_pte_cb = NULL;
+
return 0;
}

@@ -491,6 +493,7 @@ struct stage2_map_data {
struct kvm_pgtable_mm_ops *mm_ops;

int ret;
+ bool force_pte;
};

u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
@@ -613,6 +616,9 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
struct kvm_pgtable *pgt = data->mmu->pgt;
struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;

+ if (data->force_pte && (level < (KVM_PGTABLE_MAX_LEVELS - 1)))
+ return -E2BIG;
+
if (!kvm_block_mapping_supported(addr, end, phys, level))
return -E2BIG;

@@ -660,6 +666,9 @@ static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
if (data->anchor)
return 0;

+ if (data->force_pte && (level < (KVM_PGTABLE_MAX_LEVELS - 1)))
+ return 0;
+
if (!kvm_block_mapping_supported(addr, end, data->phys, level))
return 0;

@@ -791,6 +800,7 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
.memcache = mc,
.mm_ops = pgt->mm_ops,
.ret = 0,
+ .force_pte = pgt->want_pte_cb && pgt->want_pte_cb(addr, addr + size, prot),
};
struct kvm_pgtable_walker walker = {
.cb = stage2_map_walker,
@@ -826,6 +836,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
.mm_ops = pgt->mm_ops,
.owner_id = owner_id,
.ret = 0,
+ .force_pte = true,
};
struct kvm_pgtable_walker walker = {
.cb = stage2_map_walker,
@@ -1070,9 +1081,11 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size)
return kvm_pgtable_walk(pgt, addr, size, &walker);
}

-int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch,
- struct kvm_pgtable_mm_ops *mm_ops,
- enum kvm_pgtable_stage2_flags flags)
+
+int kvm_pgtable_stage2_init_full(struct kvm_pgtable *pgt, struct kvm_arch *arch,
+ struct kvm_pgtable_mm_ops *mm_ops,
+ enum kvm_pgtable_stage2_flags flags,
+ kvm_pgtable_want_pte_cb_t want_pte_cb)
{
size_t pgd_sz;
u64 vtcr = arch->vtcr;
@@ -1090,6 +1103,7 @@ int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch
pgt->mm_ops = mm_ops;
pgt->mmu = &arch->mmu;
pgt->flags = flags;
+ pgt->want_pte_cb = want_pte_cb;

/* Ensure zeroed PGD pages are visible to the hardware walker */
dsb(ishst);
--
2.32.0.402.g57bb445576-goog

Next message: Quentin Perret: "[PATCH 08/14] KVM: arm64: Add support for tagging shared pages in page-table"
Previous message: Quentin Perret: "[PATCH 06/14] KVM: arm64: Tolerate re-creating hyp mappings to set ignored bits"
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Next in thread: Marc Zyngier: "Re: [PATCH 07/14] KVM: arm64: Enable forcing page-level stage-2 mappings"
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