[PATCH v3 01/16] KVM: arm64: nv: Support multiple nested Stage-2 mmu structures

Marc Zyngier
2024-06-14T14:46:16Z

Add Stage-2 mmu data structures for virtual EL2 and for nested guests.
We don't yet populate shadow Stage-2 page tables, but we now have a
framework for getting to a shadow Stage-2 pgd.

We allocate twice the number of vcpus as Stage-2 mmu structures because
that's sufficient for each vcpu running two translation regimes without
having to flush the Stage-2 page tables.

Co-developed-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/include/asm/kvm_host.h | 36 +++++
arch/arm64/include/asm/kvm_mmu.h | 24 +++
arch/arm64/include/asm/kvm_nested.h | 6 +
arch/arm64/kvm/arm.c | 11 ++
arch/arm64/kvm/mmu.c | 69 ++++++---
arch/arm64/kvm/nested.c | 218 ++++++++++++++++++++++++++++
arch/arm64/kvm/reset.c | 6 +
7 files changed, 349 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8170c04fde91..43210a67d7eb 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -188,6 +188,33 @@ struct kvm_s2_mmu {
uint64_t split_page_chunk_size;

struct kvm_arch *arch;
+
+ /*
+ * For a shadow stage-2 MMU, the virtual vttbr used by the
+ * host to parse the guest S2.
+ * This either contains:
+ * - the virtual VTTBR programmed by the guest hypervisor with
+ * CnP cleared
+ * - The value 1 (VMID=0, BADDR=0, CnP=1) if invalid
+ *
+ * We also cache the full VTCR which gets used for TLB invalidation,
+ * taking the ARM ARM's "Any of the bits in VTCR_EL2 are permitted
+ * to be cached in a TLB" to the letter.
+ */
+ u64 tlb_vttbr;
+ u64 tlb_vtcr;
+
+ /*
+ * true when this represents a nested context where virtual
+ * HCR_EL2.VM == 1
+ */
+ bool nested_stage2_enabled;
+
+ /*
+ * 0: Nobody is currently using this, check vttbr for validity
+ * >0: Somebody is actively using this.
+ */
+ atomic_t refcnt;
};

struct kvm_arch_memory_slot {
@@ -255,6 +282,14 @@ struct kvm_arch {
*/
u64 fgu[__NR_FGT_GROUP_IDS__];

+ /*
+ * Stage 2 paging state for VMs with nested S2 using a virtual
+ * VMID.
+ */
+ struct kvm_s2_mmu *nested_mmus;
+ size_t nested_mmus_size;
+ int nested_mmus_next;
+
/* Interrupt controller */
struct vgic_dist vgic;

@@ -1283,6 +1318,7 @@ void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu);
void kvm_vcpu_put_vhe(struct kvm_vcpu *vcpu);

int __init kvm_set_ipa_limit(void);
+u32 kvm_get_pa_bits(struct kvm *kvm);

#define __KVM_HAVE_ARCH_VM_ALLOC
struct kvm *kvm_arch_alloc_vm(void);
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index d5e48d870461..87cc941cfd15 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -98,6 +98,7 @@ alternative_cb_end
#include <asm/mmu_context.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_host.h>
+#include <asm/kvm_nested.h>

void kvm_update_va_mask(struct alt_instr *alt,
__le32 *origptr, __le32 *updptr, int nr_inst);
@@ -165,6 +166,8 @@ int create_hyp_exec_mappings(phys_addr_t phys_addr, size_t size,
int create_hyp_stack(phys_addr_t phys_addr, unsigned long *haddr);
void __init free_hyp_pgds(void);

+void kvm_stage2_unmap_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size);
+
void stage2_unmap_vm(struct kvm *kvm);
int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long type);
void kvm_uninit_stage2_mmu(struct kvm *kvm);
@@ -326,5 +329,26 @@ static inline struct kvm *kvm_s2_mmu_to_kvm(struct kvm_s2_mmu *mmu)
{
return container_of(mmu->arch, struct kvm, arch);
}
+
+static inline u64 get_vmid(u64 vttbr)
+{
+ return (vttbr & VTTBR_VMID_MASK(kvm_get_vmid_bits())) >>
+ VTTBR_VMID_SHIFT;
+}
+
+static inline bool kvm_s2_mmu_valid(struct kvm_s2_mmu *mmu)
+{
+ return !(mmu->tlb_vttbr & VTTBR_CNP_BIT);
+}
+
+static inline bool kvm_is_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
+{
+ /*
+ * Be careful, mmu may not be fully initialised so do look at
+ * *any* of its fields.
+ */
+ return &kvm->arch.mmu != mmu;
+}
+
#endif /* __ASSEMBLY__ */
#endif /* __ARM64_KVM_MMU_H__ */
diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index 5e0ab0596246..a69faee31342 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -61,6 +61,12 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
}

extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
+extern void kvm_init_nested(struct kvm *kvm);
+extern int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu);
+extern void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu);
+extern struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu);
+extern void kvm_vcpu_load_hw_mmu(struct kvm_vcpu *vcpu);
+extern void kvm_vcpu_put_hw_mmu(struct kvm_vcpu *vcpu);

int kvm_init_nv_sysregs(struct kvm *kvm);

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 9996a989b52e..30ad3752e5ae 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -170,6 +170,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
mutex_unlock(&kvm->lock);
#endif

+ kvm_init_nested(kvm);
+
ret = kvm_share_hyp(kvm, kvm + 1);
if (ret)
return ret;
@@ -551,6 +553,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
struct kvm_s2_mmu *mmu;
int *last_ran;

+ if (vcpu_has_nv(vcpu))
+ kvm_vcpu_load_hw_mmu(vcpu);
+
mmu = vcpu->arch.hw_mmu;
last_ran = this_cpu_ptr(mmu->last_vcpu_ran);

@@ -601,6 +606,8 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
kvm_timer_vcpu_put(vcpu);
kvm_vgic_put(vcpu);
kvm_vcpu_pmu_restore_host(vcpu);
+ if (vcpu_has_nv(vcpu))
+ kvm_vcpu_put_hw_mmu(vcpu);
kvm_arm_vmid_clear_active();

vcpu_clear_on_unsupported_cpu(vcpu);
@@ -1459,6 +1466,10 @@ static int kvm_setup_vcpu(struct kvm_vcpu *vcpu)
if (kvm_vcpu_has_pmu(vcpu) && !kvm->arch.arm_pmu)
ret = kvm_arm_set_default_pmu(kvm);

+ /* Prepare for nested if required */
+ if (!ret && vcpu_has_nv(vcpu))
+ ret = kvm_vcpu_init_nested(vcpu);
+
return ret;
}

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 8bcab0cc3fe9..8984b7c213e1 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -328,7 +328,7 @@ static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64
may_block));
}

-static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
+void kvm_stage2_unmap_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
{
__unmap_stage2_range(mmu, start, size, true);
}
@@ -855,21 +855,9 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
.icache_inval_pou = invalidate_icache_guest_page,
};

-/**
- * kvm_init_stage2_mmu - Initialise a S2 MMU structure
- * @kvm: The pointer to the KVM structure
- * @mmu: The pointer to the s2 MMU structure
- * @type: The machine type of the virtual machine
- *
- * Allocates only the stage-2 HW PGD level table(s).
- * Note we don't need locking here as this is only called when the VM is
- * created, which can only be done once.
- */
-int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long type)
+static int kvm_init_ipa_range(struct kvm_s2_mmu *mmu, unsigned long type)
{
u32 kvm_ipa_limit = get_kvm_ipa_limit();
- int cpu, err;
- struct kvm_pgtable *pgt;
u64 mmfr0, mmfr1;
u32 phys_shift;

@@ -896,11 +884,51 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
mmfr1 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
mmu->vtcr = kvm_get_vtcr(mmfr0, mmfr1, phys_shift);

+ return 0;
+}
+
+/**
+ * kvm_init_stage2_mmu - Initialise a S2 MMU structure
+ * @kvm: The pointer to the KVM structure
+ * @mmu: The pointer to the s2 MMU structure
+ * @type: The machine type of the virtual machine
+ *
+ * Allocates only the stage-2 HW PGD level table(s).
+ * Note we don't need locking here as this is only called in two cases:
+ *
+ * - when the VM is created, which can't race against anything
+ *
+ * - when secondary kvm_s2_mmu structures are initialised for NV
+ * guests, and the caller must hold kvm->lock as this is called on a
+ * per-vcpu basis.
+ */
+int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long type)
+{
+ int cpu, err;
+ struct kvm_pgtable *pgt;
+
+ /*
+ * If we already have our page tables in place, and that the
+ * MMU context is the canonical one, we have a bug somewhere,
+ * as this is only supposed to ever happen once per VM.
+ *
+ * Otherwise, we're building nested page tables, and that's
+ * probably because userspace called KVM_ARM_VCPU_INIT more
+ * than once on the same vcpu. Since that's actually legal,
+ * don't kick a fuss and leave gracefully.
+ */
if (mmu->pgt != NULL) {
+ if (kvm_is_nested_s2_mmu(kvm, mmu))
+ return 0;
+
kvm_err("kvm_arch already initialized?\n");
return -EINVAL;
}

+ err = kvm_init_ipa_range(mmu, type);
+ if (err)
+ return err;
+
pgt = kzalloc(sizeof(*pgt), GFP_KERNEL_ACCOUNT);
if (!pgt)
return -ENOMEM;
@@ -925,6 +953,10 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t

mmu->pgt = pgt;
mmu->pgd_phys = __pa(pgt->pgd);
+
+ if (kvm_is_nested_s2_mmu(kvm, mmu))
+ kvm_init_nested_s2_mmu(mmu);
+
return 0;

out_destroy_pgtable:
@@ -976,7 +1008,7 @@ static void stage2_unmap_memslot(struct kvm *kvm,

if (!(vma->vm_flags & VM_PFNMAP)) {
gpa_t gpa = addr + (vm_start - memslot->userspace_addr);
- unmap_stage2_range(&kvm->arch.mmu, gpa, vm_end - vm_start);
+ kvm_stage2_unmap_range(&kvm->arch.mmu, gpa, vm_end - vm_start);
}
hva = vm_end;
} while (hva < reg_end);
@@ -2022,11 +2054,6 @@ void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen)
{
}

-void kvm_arch_flush_shadow_all(struct kvm *kvm)
-{
- kvm_uninit_stage2_mmu(kvm);
-}
-
void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
struct kvm_memory_slot *slot)
{
@@ -2034,7 +2061,7 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
phys_addr_t size = slot->npages << PAGE_SHIFT;

write_lock(&kvm->mmu_lock);
- unmap_stage2_range(&kvm->arch.mmu, gpa, size);
+ kvm_stage2_unmap_range(&kvm->arch.mmu, gpa, size);
write_unlock(&kvm->mmu_lock);
}

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 6813c7c7f00a..0a6b894b6390 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -7,7 +7,9 @@
#include <linux/kvm.h>
#include <linux/kvm_host.h>

+#include <asm/kvm_arm.h>
#include <asm/kvm_emulate.h>
+#include <asm/kvm_mmu.h>
#include <asm/kvm_nested.h>
#include <asm/sysreg.h>

@@ -16,6 +18,222 @@
/* Protection against the sysreg repainting madness... */
#define NV_FTR(r, f) ID_AA64##r##_EL1_##f

+/*
+ * Ratio of live shadow S2 MMU per vcpu. This is a trade-off between
+ * memory usage and potential number of different sets of S2 PTs in
+ * the guests. Running out of S2 MMUs only affects performance (we
+ * will invalidate them more often).
+ */
+#define S2_MMU_PER_VCPU 2
+
+void kvm_init_nested(struct kvm *kvm)
+{
+ kvm->arch.nested_mmus = NULL;
+ kvm->arch.nested_mmus_size = 0;
+}
+
+static int init_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
+{
+ /*
+ * We only initialise the IPA range on the canonical MMU, which
+ * defines the contract between KVM and userspace on where the
+ * "hardware" is in the IPA space. This affects the validity of MMIO
+ * exits forwarded to userspace, for example.
+ *
+ * For nested S2s, we use the PARange as exposed to the guest, as it
+ * is allowed to use it at will to expose whatever memory map it
+ * wants to its own guests as it would be on real HW.
+ */
+ return kvm_init_stage2_mmu(kvm, mmu, kvm_get_pa_bits(kvm));
+}
+
+int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_s2_mmu *tmp;
+ int num_mmus, ret = 0;
+
+ /*
+ * Let's treat memory allocation failures as benign: If we fail to
+ * allocate anything, return an error and keep the allocated array
+ * alive. Userspace may try to recover by intializing the vcpu
+ * again, and there is no reason to affect the whole VM for this.
+ */
+ num_mmus = atomic_read(&kvm->online_vcpus) * S2_MMU_PER_VCPU;
+ tmp = kvrealloc(kvm->arch.nested_mmus,
+ size_mul(sizeof(*kvm->arch.nested_mmus), kvm->arch.nested_mmus_size),
+ size_mul(sizeof(*kvm->arch.nested_mmus), num_mmus),
+ GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+ if (!tmp)
+ return -ENOMEM;
+
+ /*
+ * If we went through a realocation, adjust the MMU back-pointers in
+ * the previously initialised kvm_pgtable structures.
+ */
+ if (kvm->arch.nested_mmus != tmp)
+ for (int i = 0; i < kvm->arch.nested_mmus_size; i++)
+ tmp[i].pgt->mmu = &tmp[i];
+
+ for (int i = kvm->arch.nested_mmus_size; !ret && i < num_mmus; i++)
+ ret = init_nested_s2_mmu(kvm, &tmp[i]);
+
+ if (ret) {
+ for (int i = kvm->arch.nested_mmus_size; i < num_mmus; i++)
+ kvm_free_stage2_pgd(&tmp[i]);
+
+ return ret;
+ }
+
+ kvm->arch.nested_mmus_size = num_mmus;
+ kvm->arch.nested_mmus = tmp;
+
+ return 0;
+}
+
+struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ bool nested_stage2_enabled;
+ u64 vttbr, vtcr, hcr;
+
+ lockdep_assert_held_write(&kvm->mmu_lock);
+
+ vttbr = vcpu_read_sys_reg(vcpu, VTTBR_EL2);
+ vtcr = vcpu_read_sys_reg(vcpu, VTCR_EL2);
+ hcr = vcpu_read_sys_reg(vcpu, HCR_EL2);
+
+ nested_stage2_enabled = hcr & HCR_VM;
+
+ /* Don't consider the CnP bit for the vttbr match */
+ vttbr &= ~VTTBR_CNP_BIT;
+
+ /*
+ * Two possibilities when looking up a S2 MMU context:
+ *
+ * - either S2 is enabled in the guest, and we need a context that is
+ * S2-enabled and matches the full VTTBR (VMID+BADDR) and VTCR,
+ * which makes it safe from a TLB conflict perspective (a broken
+ * guest won't be able to generate them),
+ *
+ * - or S2 is disabled, and we need a context that is S2-disabled
+ * and matches the VMID only, as all TLBs are tagged by VMID even
+ * if S2 translation is disabled.
+ */
+ for (int i = 0; i < kvm->arch.nested_mmus_size; i++) {
+ struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
+
+ if (!kvm_s2_mmu_valid(mmu))
+ continue;
+
+ if (nested_stage2_enabled &&
+ mmu->nested_stage2_enabled &&
+ vttbr == mmu->tlb_vttbr &&
+ vtcr == mmu->tlb_vtcr)
+ return mmu;
+
+ if (!nested_stage2_enabled &&
+ !mmu->nested_stage2_enabled &&
+ get_vmid(vttbr) == get_vmid(mmu->tlb_vttbr))
+ return mmu;
+ }
+ return NULL;
+}
+
+static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_s2_mmu *s2_mmu;
+ int i;
+
+ lockdep_assert_held_write(&vcpu->kvm->mmu_lock);
+
+ s2_mmu = lookup_s2_mmu(vcpu);
+ if (s2_mmu)
+ goto out;
+
+ /*
+ * Make sure we don't always search from the same point, or we
+ * will always reuse a potentially active context, leaving
+ * free contexts unused.
+ */
+ for (i = kvm->arch.nested_mmus_next;
+ i < (kvm->arch.nested_mmus_size + kvm->arch.nested_mmus_next);
+ i++) {
+ s2_mmu = &kvm->arch.nested_mmus[i % kvm->arch.nested_mmus_size];
+
+ if (atomic_read(&s2_mmu->refcnt) == 0)
+ break;
+ }
+ BUG_ON(atomic_read(&s2_mmu->refcnt)); /* We have struct MMUs to spare */
+
+ /* Set the scene for the next search */
+ kvm->arch.nested_mmus_next = (i + 1) % kvm->arch.nested_mmus_size;
+
+ /* Clear the old state */
+ if (kvm_s2_mmu_valid(s2_mmu))
+ kvm_stage2_unmap_range(s2_mmu, 0, kvm_phys_size(s2_mmu));
+
+ /*
+ * The virtual VMID (modulo CnP) will be used as a key when matching
+ * an existing kvm_s2_mmu.
+ *
+ * We cache VTCR at allocation time, once and for all. It'd be great
+ * if the guest didn't screw that one up, as this is not very
+ * forgiving...
+ */
+ s2_mmu->tlb_vttbr = vcpu_read_sys_reg(vcpu, VTTBR_EL2) & ~VTTBR_CNP_BIT;
+ s2_mmu->tlb_vtcr = vcpu_read_sys_reg(vcpu, VTCR_EL2);
+ s2_mmu->nested_stage2_enabled = vcpu_read_sys_reg(vcpu, HCR_EL2) & HCR_VM;
+
+out:
+ atomic_inc(&s2_mmu->refcnt);
+ return s2_mmu;
+}
+
+void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu)
+{
+ /* CnP being set denotes an invalid entry */
+ mmu->tlb_vttbr = VTTBR_CNP_BIT;
+ mmu->nested_stage2_enabled = false;
+ atomic_set(&mmu->refcnt, 0);
+}
+
+void kvm_vcpu_load_hw_mmu(struct kvm_vcpu *vcpu)
+{
+ if (is_hyp_ctxt(vcpu)) {
+ vcpu->arch.hw_mmu = &vcpu->kvm->arch.mmu;
+ } else {
+ write_lock(&vcpu->kvm->mmu_lock);
+ vcpu->arch.hw_mmu = get_s2_mmu_nested(vcpu);
+ write_unlock(&vcpu->kvm->mmu_lock);
+ }
+}
+
+void kvm_vcpu_put_hw_mmu(struct kvm_vcpu *vcpu)
+{
+ if (kvm_is_nested_s2_mmu(vcpu->kvm, vcpu->arch.hw_mmu)) {
+ atomic_dec(&vcpu->arch.hw_mmu->refcnt);
+ vcpu->arch.hw_mmu = NULL;
+ }
+}
+
+void kvm_arch_flush_shadow_all(struct kvm *kvm)
+{
+ int i;
+
+ for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
+ struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
+
+ if (!WARN_ON(atomic_read(&mmu->refcnt)))
+ kvm_free_stage2_pgd(mmu);
+ }
+ kfree(kvm->arch.nested_mmus);
+ kvm->arch.nested_mmus = NULL;
+ kvm->arch.nested_mmus_size = 0;
+ kvm_uninit_stage2_mmu(kvm);
+}
+
/*
* Our emulated CPU doesn't support all the possible features. For the
* sake of simplicity (and probably mental sanity), wipe out a number
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 1b7b58cb121f..621bc0dcfd0a 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -265,6 +265,12 @@ void kvm_reset_vcpu(struct kvm_vcpu *vcpu)
preempt_enable();
}

+u32 kvm_get_pa_bits(struct kvm *kvm)
+{
+ /* Fixed limit until we can configure ID_AA64MMFR0.PARange */
+ return kvm_ipa_limit;
+}
+
u32 get_kvm_ipa_limit(void)
{
return kvm_ipa_limit;
--
2.39.2