[PATCH v4 14/25] KVM: arm64: Add per-cpu fixmap infrastructure at EL2

Will Deacon
2022-10-17T11:59:17Z

From: Quentin Perret <qperret@google.com>

Mapping pages in a guest page-table from within the pKVM hypervisor at
EL2 may require cache maintenance to ensure that the initialised page
contents is visible even to non-cacheable (e.g. MMU-off) accesses from
the guest.

In preparation for performing this maintenance at EL2, introduce a
per-vCPU fixmap which allows the pKVM hypervisor to map guest pages
temporarily into its stage-1 page-table for the purposes of cache
maintenance and, in future, poisoning on the reclaim path. The use of a
fixmap avoids the need for memory allocation or locking on the map()
path.

Tested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_pgtable.h | 14 +++
arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 2 +
arch/arm64/kvm/hyp/include/nvhe/mm.h | 4 +
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 1 -
arch/arm64/kvm/hyp/nvhe/mm.c | 94 +++++++++++++++++++
arch/arm64/kvm/hyp/nvhe/setup.c | 4 +
arch/arm64/kvm/hyp/pgtable.c | 12 ---
7 files changed, 118 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 4f6d79fe4352..b2a886c9e78d 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -30,6 +30,8 @@ typedef u64 kvm_pte_t;
#define KVM_PTE_ADDR_MASK GENMASK(47, PAGE_SHIFT)
#define KVM_PTE_ADDR_51_48 GENMASK(15, 12)

+#define KVM_PHYS_INVALID (-1ULL)
+
static inline bool kvm_pte_valid(kvm_pte_t pte)
{
return pte & KVM_PTE_VALID;
@@ -45,6 +47,18 @@ static inline u64 kvm_pte_to_phys(kvm_pte_t pte)
return pa;
}

+static inline kvm_pte_t kvm_phys_to_pte(u64 pa)
+{
+ kvm_pte_t pte = pa & KVM_PTE_ADDR_MASK;
+
+ if (PAGE_SHIFT == 16) {
+ pa &= GENMASK(51, 48);
+ pte |= FIELD_PREP(KVM_PTE_ADDR_51_48, pa >> 48);
+ }
+
+ return pte;
+}
+
static inline u64 kvm_granule_shift(u32 level)
{
/* Assumes KVM_PGTABLE_MAX_LEVELS is 4 */
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index ce9a796a85ee..ef31a1872c93 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -59,6 +59,8 @@ enum pkvm_component_id {
PKVM_ID_HYP,
};

+extern unsigned long hyp_nr_cpus;
+
int __pkvm_prot_finalize(void);
int __pkvm_host_share_hyp(u64 pfn);
int __pkvm_host_unshare_hyp(u64 pfn);
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
index b2ee6d5df55b..d5ec972b5c1e 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
@@ -13,6 +13,10 @@
extern struct kvm_pgtable pkvm_pgtable;
extern hyp_spinlock_t pkvm_pgd_lock;

+int hyp_create_pcpu_fixmap(void);
+void *hyp_fixmap_map(phys_addr_t phys);
+void hyp_fixmap_unmap(void);
+
int hyp_create_idmap(u32 hyp_va_bits);
int hyp_map_vectors(void);
int hyp_back_vmemmap(phys_addr_t back);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 2ef6aaa21ba5..1c38451050e5 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -21,7 +21,6 @@

#define KVM_HOST_S2_FLAGS (KVM_PGTABLE_S2_NOFWB | KVM_PGTABLE_S2_IDMAP)

-extern unsigned long hyp_nr_cpus;
struct host_mmu host_mmu;

static struct hyp_pool host_s2_pool;
diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index d3a3b47181de..b77215630d5c 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -14,6 +14,7 @@
#include <nvhe/early_alloc.h>
#include <nvhe/gfp.h>
#include <nvhe/memory.h>
+#include <nvhe/mem_protect.h>
#include <nvhe/mm.h>
#include <nvhe/spinlock.h>

@@ -25,6 +26,12 @@ unsigned int hyp_memblock_nr;

static u64 __io_map_base;

+struct hyp_fixmap_slot {
+ u64 addr;
+ kvm_pte_t *ptep;
+};
+static DEFINE_PER_CPU(struct hyp_fixmap_slot, fixmap_slots);
+
static int __pkvm_create_mappings(unsigned long start, unsigned long size,
unsigned long phys, enum kvm_pgtable_prot prot)
{
@@ -212,6 +219,93 @@ int hyp_map_vectors(void)
return 0;
}

+void *hyp_fixmap_map(phys_addr_t phys)
+{
+ struct hyp_fixmap_slot *slot = this_cpu_ptr(&fixmap_slots);
+ kvm_pte_t pte, *ptep = slot->ptep;
+
+ pte = *ptep;
+ pte &= ~kvm_phys_to_pte(KVM_PHYS_INVALID);
+ pte |= kvm_phys_to_pte(phys) | KVM_PTE_VALID;
+ WRITE_ONCE(*ptep, pte);
+ dsb(nshst);
+
+ return (void *)slot->addr;
+}
+
+static void fixmap_clear_slot(struct hyp_fixmap_slot *slot)
+{
+ kvm_pte_t *ptep = slot->ptep;
+ u64 addr = slot->addr;
+
+ WRITE_ONCE(*ptep, *ptep & ~KVM_PTE_VALID);
+ dsb(nshst);
+ __tlbi_level(vale2, __TLBI_VADDR(addr, 0), (KVM_PGTABLE_MAX_LEVELS - 1));
+ dsb(nsh);
+ isb();
+}
+
+void hyp_fixmap_unmap(void)
+{
+ fixmap_clear_slot(this_cpu_ptr(&fixmap_slots));
+}
+
+static int __create_fixmap_slot_cb(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
+ enum kvm_pgtable_walk_flags flag,
+ void * const arg)
+{
+ struct hyp_fixmap_slot *slot = per_cpu_ptr(&fixmap_slots, (u64)arg);
+
+ if (!kvm_pte_valid(*ptep) || level != KVM_PGTABLE_MAX_LEVELS - 1)
+ return -EINVAL;
+
+ slot->addr = addr;
+ slot->ptep = ptep;
+
+ /*
+ * Clear the PTE, but keep the page-table page refcount elevated to
+ * prevent it from ever being freed. This lets us manipulate the PTEs
+ * by hand safely without ever needing to allocate memory.
+ */
+ fixmap_clear_slot(slot);
+
+ return 0;
+}
+
+static int create_fixmap_slot(u64 addr, u64 cpu)
+{
+ struct kvm_pgtable_walker walker = {
+ .cb = __create_fixmap_slot_cb,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ .arg = (void *)cpu,
+ };
+
+ return kvm_pgtable_walk(&pkvm_pgtable, addr, PAGE_SIZE, &walker);
+}
+
+int hyp_create_pcpu_fixmap(void)
+{
+ unsigned long addr, i;
+ int ret;
+
+ for (i = 0; i < hyp_nr_cpus; i++) {
+ ret = pkvm_alloc_private_va_range(PAGE_SIZE, &addr);
+ if (ret)
+ return ret;
+
+ ret = kvm_pgtable_hyp_map(&pkvm_pgtable, addr, PAGE_SIZE,
+ __hyp_pa(__hyp_bss_start), PAGE_HYP);
+ if (ret)
+ return ret;
+
+ ret = create_fixmap_slot(addr, i);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+
int hyp_create_idmap(u32 hyp_va_bits)
{
unsigned long start, end;
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 2be72fbe7279..0f69c1393416 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -321,6 +321,10 @@ void __noreturn __pkvm_init_finalise(void)
if (ret)
goto out;

+ ret = hyp_create_pcpu_fixmap();
+ if (ret)
+ goto out;
+
pkvm_hyp_vm_table_init(vm_table_base);
out:
/*
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index a1a27f88a312..2bcb2d5903ba 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -57,8 +57,6 @@ struct kvm_pgtable_walk_data {
u64 end;
};

-#define KVM_PHYS_INVALID (-1ULL)
-
static bool kvm_phys_is_valid(u64 phys)
{
return phys < BIT(id_aa64mmfr0_parange_to_phys_shift(ID_AA64MMFR0_EL1_PARANGE_MAX));
@@ -122,16 +120,6 @@ static bool kvm_pte_table(kvm_pte_t pte, u32 level)
return FIELD_GET(KVM_PTE_TYPE, pte) == KVM_PTE_TYPE_TABLE;
}

-static kvm_pte_t kvm_phys_to_pte(u64 pa)
-{
- kvm_pte_t pte = pa & KVM_PTE_ADDR_MASK;
-
- if (PAGE_SHIFT == 16)
- pte |= FIELD_PREP(KVM_PTE_ADDR_51_48, pa >> 48);
-
- return pte;
-}
-
static kvm_pte_t *kvm_pte_follow(kvm_pte_t pte, struct kvm_pgtable_mm_ops *mm_ops)
{
return mm_ops->phys_to_virt(kvm_pte_to_phys(pte));
--
2.38.0.413.g74048e4d9e-goog