[PATCH v2 15/15] KVM: arm64: pkvm: Unshare guest structs during teardown

Quentin Perret
2021-10-19T12:13:58Z

Make use of the newly introduced unshare hypercall during guest teardown
to unmap guest-related data structures from the hyp stage-1.

Signed-off-by: Quentin Perret <qperret@google.com>
---
arch/arm64/include/asm/kvm_host.h | 2 ++
arch/arm64/include/asm/kvm_mmu.h | 1 +
arch/arm64/kvm/arm.c | 2 ++
arch/arm64/kvm/fpsimd.c | 29 +++++++++++++++++++++
arch/arm64/kvm/mmu.c | 42 +++++++++++++++++++++++++++++++
arch/arm64/kvm/reset.c | 8 +++++-
6 files changed, 83 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index d1451c8a768b..9f70e82c7436 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -323,6 +323,7 @@ struct kvm_vcpu_arch {

struct thread_info *host_thread_info; /* hyp VA */
struct user_fpsimd_state *host_fpsimd_state; /* hyp VA */
+ struct task_struct *parent_task;

struct {
/* {Break,watch}point registers */
@@ -738,6 +739,7 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu);
void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu);
void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu);
+void kvm_vcpu_unshare_task_fp(struct kvm_vcpu *vcpu);

static inline bool kvm_pmu_counter_deferred(struct perf_event_attr *attr)
{
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 185d0f62b724..81839e9a8a24 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -151,6 +151,7 @@ static __always_inline unsigned long __kern_hyp_va(unsigned long v)
#include <asm/stage2_pgtable.h>

int kvm_share_hyp(void *from, void *to);
+void kvm_unshare_hyp(void *from, void *to);
int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
int create_hyp_io_mappings(phys_addr_t phys_addr, size_t size,
void __iomem **kaddr,
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 5312d5a2ef69..ebab9529b736 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -188,6 +188,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
}
}
atomic_set(&kvm->online_vcpus, 0);
+
+ kvm_unshare_hyp(kvm, kvm + 1);
}

int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 2fe1128d9f3d..ace5ebef8aab 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -15,6 +15,22 @@
#include <asm/kvm_mmu.h>
#include <asm/sysreg.h>

+void kvm_vcpu_unshare_task_fp(struct kvm_vcpu *vcpu)
+{
+ struct task_struct *p = vcpu->arch.parent_task;
+ struct user_fpsimd_state *fpsimd;
+ struct thread_info *ti;
+
+ if (!is_protected_kvm_enabled() || !p)
+ return;
+
+ ti = &p->thread_info;
+ kvm_unshare_hyp(ti, ti + 1);
+ fpsimd = &p->thread.uw.fpsimd_state;
+ kvm_unshare_hyp(fpsimd, fpsimd + 1);
+ put_task_struct(p);
+}
+
/*
* Called on entry to KVM_RUN unless this vcpu previously ran at least
* once and the most recent prior KVM_RUN for this vcpu was called from
@@ -31,6 +47,8 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
struct thread_info *ti = &current->thread_info;
struct user_fpsimd_state *fpsimd = &current->thread.uw.fpsimd_state;

+ kvm_vcpu_unshare_task_fp(vcpu);
+
/*
* Make sure the host task thread flags and fpsimd state are
* visible to hyp:
@@ -45,6 +63,17 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)

vcpu->arch.host_thread_info = kern_hyp_va(ti);
vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
+
+ /*
+ * We need to keep current's task_struct pinned until its data has been
+ * unshared with the hypervisor to make sure it is not re-used by the
+ * kernel and donated to someone else while already shared -- see
+ * kvm_vcpu_unshare_task_fp() for the matching put_task_struct().
+ */
+ if (is_protected_kvm_enabled()) {
+ get_task_struct(current);
+ vcpu->arch.parent_task = current;
+ }
error:
return ret;
}
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index f0c16ed95974..d548141da2ea 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -344,6 +344,32 @@ static int share_pfn_hyp(u64 pfn)
return ret;
}

+static int unshare_pfn_hyp(u64 pfn)
+{
+ struct rb_node **node, *parent;
+ struct hyp_shared_pfn *this;
+ int ret = 0;
+
+ mutex_lock(&hyp_shared_pfns_lock);
+ this = find_shared_pfn(pfn, &node, &parent);
+ if (WARN_ON(!this)) {
+ ret = -EINVAL;
+ goto unlock;
+ }
+
+ this->count--;
+ if (this->count)
+ goto unlock;
+
+ rb_erase(&this->node, &hyp_shared_pfns);
+ kfree(this);
+ ret = kvm_call_hyp_nvhe(__pkvm_host_unshare_hyp, pfn, 1);
+unlock:
+ mutex_unlock(&hyp_shared_pfns_lock);
+
+ return ret;
+}
+
int kvm_share_hyp(void *from, void *to)
{
phys_addr_t start, end, cur;
@@ -368,6 +394,22 @@ int kvm_share_hyp(void *from, void *to)
return 0;
}

+void kvm_unshare_hyp(void *from, void *to)
+{
+ phys_addr_t start, end, cur;
+ u64 pfn;
+
+ if (is_kernel_in_hyp_mode() || kvm_host_owns_hyp_mappings() || !from)
+ return;
+
+ start = ALIGN_DOWN(kvm_kaddr_to_phys(from), PAGE_SIZE);
+ end = PAGE_ALIGN(kvm_kaddr_to_phys(to));
+ for (cur = start; cur < end; cur += PAGE_SIZE) {
+ pfn = __phys_to_pfn(cur);
+ WARN_ON(unshare_pfn_hyp(pfn));
+ }
+}
+
/**
* create_hyp_mappings - duplicate a kernel virtual address range in Hyp mode
* @from: The virtual kernel start address of the range
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index cf781ec9212a..bf15e9de4123 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -150,7 +150,13 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu)

void kvm_arm_vcpu_destroy(struct kvm_vcpu *vcpu)
{
- kfree(vcpu->arch.sve_state);
+ void *sve_state = vcpu->arch.sve_state;
+
+ kvm_vcpu_unshare_task_fp(vcpu);
+ kvm_unshare_hyp(vcpu, vcpu + 1);
+ if (sve_state)
+ kvm_unshare_hyp(sve_state, sve_state + vcpu_sve_state_size(vcpu));
+ kfree(sve_state);
}

static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu)
--
2.33.0.1079.g6e70778dc9-goog