[PATCH v6 34/64] KVM: arm64: nv: Support multiple nested Stage-2 mmu structures

Marc Zyngier
2022-01-28T12:50:58Z

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 | 29 +++++
arch/arm64/include/asm/kvm_mmu.h | 9 ++
arch/arm64/include/asm/kvm_nested.h | 7 +
arch/arm64/kvm/arm.c | 16 ++-
arch/arm64/kvm/mmu.c | 29 +++--
arch/arm64/kvm/nested.c | 195 ++++++++++++++++++++++++++++
6 files changed, 275 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index fa253f08e0fd..a15183d0e1bf 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -101,14 +101,43 @@ struct kvm_s2_mmu {
int __percpu *last_vcpu_ran;

struct kvm_arch *arch;
+
+ /*
+ * For a shadow stage-2 MMU, the virtual vttbr programmed by the guest
+ * hypervisor. Unused for kvm_arch->mmu. Set to 1 when the structure
+ * contains no valid information.
+ */
+ u64 vttbr;
+
+ /* 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;
};

+static inline bool kvm_s2_mmu_valid(struct kvm_s2_mmu *mmu)
+{
+ return !(mmu->vttbr & 1);
+}
+
struct kvm_arch_memory_slot {
};

struct kvm_arch {
struct kvm_s2_mmu mmu;

+ /*
+ * Stage 2 paging stage for VMs with nested virtual using a virtual
+ * VMID.
+ */
+ struct kvm_s2_mmu *nested_mmus;
+ size_t nested_mmus_size;
+ int nested_mmus_next;
+
/* VTCR_EL2 value for this VM */
u64 vtcr;

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 1b314b2a69bc..0750d022bbf8 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -116,6 +116,7 @@ alternative_cb_end
#include <asm/cacheflush.h>
#include <asm/mmu_context.h>
#include <asm/kvm_emulate.h>
+#include <asm/kvm_nested.h>

void kvm_update_va_mask(struct alt_instr *alt,
__le32 *origptr, __le32 *updptr, int nr_inst);
@@ -161,6 +162,7 @@ int create_hyp_exec_mappings(phys_addr_t phys_addr, size_t size,
void **haddr);
void free_hyp_pgds(void);

+void kvm_unmap_stage2_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);
void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu);
@@ -296,5 +298,12 @@ 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;
+}
+
#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 7d398510fd9d..8bb7159f2b6b 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -65,6 +65,13 @@ static inline u64 translate_cnthctl_el2_to_cntkctl_el1(u64 cnthctl)
(cnthctl & (CNTHCTL_EVNTI | CNTHCTL_EVNTDIR | CNTHCTL_EVNTEN)));
}

+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 *kvm, u64 vttbr, u64 hcr);
+extern void kvm_vcpu_load_hw_mmu(struct kvm_vcpu *vcpu);
+extern void kvm_vcpu_put_hw_mmu(struct kvm_vcpu *vcpu);
+
int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe);
extern bool __forward_traps(struct kvm_vcpu *vcpu, unsigned int reg,
u64 control_bit);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 06ca11e90482..14f85f1e15b2 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -37,6 +37,7 @@
#include <asm/kvm_arm.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_mmu.h>
+#include <asm/kvm_nested.h>
#include <asm/kvm_emulate.h>
#include <asm/sections.h>

@@ -146,6 +147,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
if (ret)
return ret;

+ kvm_init_nested(kvm);
+
ret = kvm_share_hyp(kvm, kvm + 1);
if (ret)
goto out_free_stage2_pgd;
@@ -375,6 +378,9 @@ 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);

@@ -423,6 +429,9 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
kvm_vgic_put(vcpu);
kvm_vcpu_pmu_restore_host(vcpu);

+ if (vcpu_has_nv(vcpu))
+ kvm_vcpu_put_hw_mmu(vcpu);
+
vcpu->cpu = -1;
}

@@ -1122,8 +1131,13 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,

vcpu->arch.target = phys_target;

+ /* Prepare for nested if required */
+ ret = kvm_vcpu_init_nested(vcpu);
+
/* Now we know what it is, we can reset it. */
- ret = kvm_reset_vcpu(vcpu);
+ if (!ret)
+ ret = kvm_reset_vcpu(vcpu);
+
if (ret) {
vcpu->arch.target = -1;
bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index bc2aba953299..55525fd5743d 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -162,7 +162,7 @@ static void invalidate_icache_guest_page(void *va, size_t size)
* does.
*/
/**
- * unmap_stage2_range -- Clear stage2 page table entries to unmap a range
+ * __unmap_stage2_range -- Clear stage2 page table entries to unmap a range
* @mmu: The KVM stage-2 MMU pointer
* @start: The intermediate physical base address of the range to unmap
* @size: The size of the area to unmap
@@ -185,7 +185,7 @@ 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_unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
{
__unmap_stage2_range(mmu, start, size, true);
}
@@ -628,7 +628,20 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
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->arch.mmu != mmu)
+ return 0;
+
kvm_err("kvm_arch already initialized?\n");
return -EINVAL;
}
@@ -654,6 +667,9 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
mmu->pgt = pgt;
mmu->pgd_phys = __pa(pgt->pgd);
WRITE_ONCE(mmu->vmid.vmid_gen, 0);
+
+ kvm_init_nested_s2_mmu(mmu);
+
return 0;

out_destroy_pgtable:
@@ -699,7 +715,7 @@ 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_unmap_stage2_range(&kvm->arch.mmu, gpa, vm_end - vm_start);
}
hva = vm_end;
} while (hva < reg_end);
@@ -1681,11 +1697,6 @@ void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen)
{
}

-void kvm_arch_flush_shadow_all(struct kvm *kvm)
-{
- kvm_free_stage2_pgd(&kvm->arch.mmu);
-}
-
void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
struct kvm_memory_slot *slot)
{
@@ -1693,7 +1704,7 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
phys_addr_t size = slot->npages << PAGE_SHIFT;

spin_lock(&kvm->mmu_lock);
- unmap_stage2_range(&kvm->arch.mmu, gpa, size);
+ kvm_unmap_stage2_range(&kvm->arch.mmu, gpa, size);
spin_unlock(&kvm->mmu_lock);
}

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 254152cd791e..bfa2b9229173 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -7,12 +7,189 @@
#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>

#include "sys_regs.h"

+void kvm_init_nested(struct kvm *kvm)
+{
+ kvm->arch.nested_mmus = NULL;
+ kvm->arch.nested_mmus_size = 0;
+}
+
+int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct kvm_s2_mmu *tmp;
+ int num_mmus;
+ int ret = -ENOMEM;
+
+ if (!test_bit(KVM_ARM_VCPU_HAS_EL2, vcpu->arch.features))
+ return 0;
+
+ if (!cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
+ return -EINVAL;
+
+ mutex_lock(&kvm->lock);
+
+ /*
+ * 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) * 2;
+ tmp = krealloc(kvm->arch.nested_mmus,
+ num_mmus * sizeof(*kvm->arch.nested_mmus),
+ GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+ if (tmp) {
+ /*
+ * If we went through a realocation, adjust the MMU
+ * back-pointers in the previously initialised
+ * pg_table structures.
+ */
+ if (kvm->arch.nested_mmus != tmp) {
+ int i;
+
+ for (i = 0; i < num_mmus - 2; i++)
+ tmp[i].pgt->mmu = &tmp[i];
+ }
+
+ if (kvm_init_stage2_mmu(kvm, &tmp[num_mmus - 1]) ||
+ kvm_init_stage2_mmu(kvm, &tmp[num_mmus - 2])) {
+ kvm_free_stage2_pgd(&tmp[num_mmus - 1]);
+ kvm_free_stage2_pgd(&tmp[num_mmus - 2]);
+ } else {
+ kvm->arch.nested_mmus_size = num_mmus;
+ ret = 0;
+ }
+
+ kvm->arch.nested_mmus = tmp;
+ }
+
+ mutex_unlock(&kvm->lock);
+ return ret;
+}
+
+/* Must be called with kvm->lock held */
+struct kvm_s2_mmu *lookup_s2_mmu(struct kvm *kvm, u64 vttbr, u64 hcr)
+{
+ bool nested_stage2_enabled = hcr & HCR_VM;
+ int i;
+
+ /* Don't consider the CnP bit for the vttbr match */
+ vttbr = 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), 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 (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->vttbr)
+ return mmu;
+
+ if (!nested_stage2_enabled &&
+ !mmu->nested_stage2_enabled &&
+ get_vmid(vttbr) == get_vmid(mmu->vttbr))
+ return mmu;
+ }
+ return NULL;
+}
+
+static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ u64 vttbr = vcpu_read_sys_reg(vcpu, VTTBR_EL2);
+ u64 hcr= vcpu_read_sys_reg(vcpu, HCR_EL2);
+ struct kvm_s2_mmu *s2_mmu;
+ int i;
+
+ s2_mmu = lookup_s2_mmu(kvm, vttbr, hcr);
+ 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;
+
+ if (kvm_s2_mmu_valid(s2_mmu)) {
+ /* Clear the old state */
+ kvm_unmap_stage2_range(s2_mmu, 0, kvm_phys_size(kvm));
+ if (s2_mmu->vmid.vmid_gen)
+ kvm_call_hyp(__kvm_tlb_flush_vmid, s2_mmu);
+ }
+
+ /*
+ * The virtual VMID (modulo CnP) will be used as a key when matching
+ * an existing kvm_s2_mmu.
+ */
+ s2_mmu->vttbr = vttbr & ~VTTBR_CNP_BIT;
+ s2_mmu->nested_stage2_enabled = hcr & HCR_VM;
+
+out:
+ atomic_inc(&s2_mmu->refcnt);
+ return s2_mmu;
+}
+
+void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu)
+{
+ mmu->vttbr = 1;
+ 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 {
+ spin_lock(&vcpu->kvm->mmu_lock);
+ vcpu->arch.hw_mmu = get_s2_mmu_nested(vcpu);
+ spin_unlock(&vcpu->kvm->mmu_lock);
+ }
+}
+
+void kvm_vcpu_put_hw_mmu(struct kvm_vcpu *vcpu)
+{
+ if (vcpu->arch.hw_mmu != &vcpu->kvm->arch.mmu) {
+ atomic_dec(&vcpu->arch.hw_mmu->refcnt);
+ vcpu->arch.hw_mmu = NULL;
+ }
+}
+
/*
* Inject wfx to the virtual EL2 if this is not from the virtual EL2 and
* the virtual HCR_EL2.TWX is set. Otherwise, let the host hypervisor
@@ -31,6 +208,24 @@ int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe)
return -EINVAL;
}

+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];
+
+ WARN_ON(atomic_read(&mmu->refcnt));
+
+ if (!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_free_stage2_pgd(&kvm->arch.mmu);
+}
+
/*
* Our emulated CPU doesn't support all the possible features. For the
* sake of simplicity (and probably mental sanity), wipe out a number