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KVM: arm64: nv: Expose shadow page tables in debugfs

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Exposing shadow page tables in debugfs improves the debugability and
testability of NV. With this patch a new directory "nested" is created
for each VM created if the host is NV capable. Within the directory each
valid s2 mmu will have its shadow page table exposed as a readable file
with the file name formatted as 0x<vttbr>-0x<vtcr>-s2-{en,dis}abled. The
creation and removal of the files happen at the points when an s2 mmu
becomes valid, or the context it represents change. In the future the
"nested" directory can also hold other NV related information.

This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS.

Suggested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Sebastian Ene <sebastianene@google.com>
Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://patch.msgid.link/20260317182638.1592507-3-weilin.chang@arm.com
[maz: minor refactor, full 16 chars addresses]
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Wei-Lin Chang
2026-03-17 18:26:38 +00:00
committed by Marc Zyngier
parent 204f7c018d
commit 19e15dc73f
4 changed files with 44 additions and 1 deletions
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9
arch/arm64/include/asm/kvm_host.h
View File

@@ -217,6 +217,10 @@ struct kvm_s2_mmu {
*/
bool nested_stage2_enabled;
#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
struct dentry *shadow_pt_debugfs_dentry;
#endif
/*
* true when this MMU needs to be unmapped before being used for a new
* purpose.
@@ -405,6 +409,11 @@ struct kvm_arch {
* the associated pKVM instance in the hypervisor.
*/
struct kvm_protected_vm pkvm;
#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
/* Nested virtualization info */
struct dentry *debugfs_nv_dentry;
#endif
};
struct kvm_vcpu_fault_info {

4
arch/arm64/include/asm/kvm_mmu.h
View File

@@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void)
#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu);
void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu);
#else
static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {}
static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {}
#endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
#endif /* __ASSEMBLER__ */

6
arch/arm64/kvm/nested.c
View File

@@ -730,8 +730,10 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu)
kvm->arch.nested_mmus_next = (i + 1) % kvm->arch.nested_mmus_size;
/* Make sure we don't forget to do the laundry */
if (kvm_s2_mmu_valid(s2_mmu))
if (kvm_s2_mmu_valid(s2_mmu)) {
kvm_nested_s2_ptdump_remove_debugfs(s2_mmu);
s2_mmu->pending_unmap = true;
}
/*
* The virtual VMID (modulo CnP) will be used as a key when matching
@@ -745,6 +747,8 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu)
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;
kvm_nested_s2_ptdump_create_debugfs(s2_mmu);
out:
atomic_inc(&s2_mmu->refcnt);

26
arch/arm64/kvm/ptdump.c
View File

@@ -10,12 +10,14 @@
#include <linux/kvm_host.h>
#include <linux/seq_file.h>
#include <asm/cpufeature.h>
#include <asm/kvm_mmu.h>
#include <asm/kvm_pgtable.h>
#include <asm/ptdump.h>
#define MARKERS_LEN 2
#define KVM_PGTABLE_MAX_LEVELS (KVM_PGTABLE_LAST_LEVEL + 1)
#define S2FNAMESZ sizeof("0x0123456789abcdef-0x0123456789abcdef-s2-disabled")
struct kvm_ptdump_guest_state {
struct kvm_s2_mmu *mmu;
@@ -277,6 +279,28 @@ static const struct file_operations kvm_pgtable_levels_fops = {
.release = kvm_pgtable_debugfs_close,
};
void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
{
struct dentry *dent;
char file_name[S2FNAMESZ];
snprintf(file_name, sizeof(file_name), "0x%016llx-0x%016llx-s2-%sabled",
mmu->tlb_vttbr,
mmu->tlb_vtcr,
mmu->nested_stage2_enabled ? "en" : "dis");
dent = debugfs_create_file(file_name, 0400,
mmu->arch->debugfs_nv_dentry, mmu,
&kvm_ptdump_guest_fops);
mmu->shadow_pt_debugfs_dentry = dent;
}
void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
{
debugfs_remove(mmu->shadow_pt_debugfs_dentry);
}
void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
{
debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
@@ -285,4 +309,6 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
&kvm->arch.mmu, &kvm_pgtable_range_fops);
debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
&kvm->arch.mmu, &kvm_pgtable_levels_fops);
if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
kvm->arch.debugfs_nv_dentry = debugfs_create_dir("nested", kvm->debugfs_dentry);
}