[PATCH v2 21/27] KVM: x86/mmu: Drop infrastructure for multiple page-track modes

From: Sean Christopherson
Date: Fri Mar 10 2023 - 19:25:43 EST

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Drop "support" for multiple page-track modes, as there is no evidence
that array-based and refcounted metadata is the optimal solution for
other modes, nor is there any evidence that other use cases, e.g. for
access-tracking, will be a good fit for the page-track machinery in
general.

E.g. one potential use case of access-tracking would be to prevent guest
access to poisoned memory (from the guest's perspective). In that case,
the number of poisoned pages is likely to be a very small percentage of
the guest memory, and there is no need to reference count the number of
access-tracking users, i.e. expanding gfn_track[] for a new mode would be
grossly inefficient. And for poisoned memory, host userspace would also
likely want to trap accesses, e.g. to inject #MC into the guest, and that
isn't currently supported by the page-track framework.

A better alternative for that poisoned page use case is likely a
variation of the proposed per-gfn attributes overlay (linked), which
would allow efficiently tracking the sparse set of poisoned pages, and by
default would exit to userspace on access.

Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@xxxxxxxxxx
Cc: Ben Gardon <bgardon@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 12 +--
arch/x86/include/asm/kvm_page_track.h | 11 +--
arch/x86/kvm/mmu/mmu.c | 14 ++--
arch/x86/kvm/mmu/page_track.c | 111 ++++++++------------------
arch/x86/kvm/mmu/page_track.h | 3 +-
drivers/gpu/drm/i915/gvt/kvmgt.c | 4 +-
6 files changed, 51 insertions(+), 104 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a3423711e403..23567b851864 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -288,13 +288,13 @@ struct kvm_kernel_irq_routing_entry;
* kvm_mmu_page_role tracks the properties of a shadow page (where shadow page
* also includes TDP pages) to determine whether or not a page can be used in
* the given MMU context. This is a subset of the overall kvm_cpu_role to
- * minimize the size of kvm_memory_slot.arch.gfn_track, i.e. allows allocating
- * 2 bytes per gfn instead of 4 bytes per gfn.
+ * minimize the size of kvm_memory_slot.arch.gfn_write_track, i.e. allows
+ * allocating 2 bytes per gfn instead of 4 bytes per gfn.
*
* Upper-level shadow pages having gptes are tracked for write-protection via
- * gfn_track. As above, gfn_track is a 16 bit counter, so KVM must not create
- * more than 2^16-1 upper-level shadow pages at a single gfn, otherwise
- * gfn_track will overflow and explosions will ensure.
+ * gfn_write_track. As above, gfn_write_track is a 16 bit counter, so KVM must
+ * not create more than 2^16-1 upper-level shadow pages at a single gfn,
+ * otherwise gfn_write_track will overflow and explosions will ensue.
*
* A unique shadow page (SP) for a gfn is created if and only if an existing SP
* cannot be reused. The ability to reuse a SP is tracked by its role, which
@@ -1023,7 +1023,7 @@ struct kvm_lpage_info {
struct kvm_arch_memory_slot {
struct kvm_rmap_head *rmap[KVM_NR_PAGE_SIZES];
struct kvm_lpage_info *lpage_info[KVM_NR_PAGE_SIZES - 1];
- unsigned short *gfn_track[KVM_PAGE_TRACK_MAX];
+ unsigned short *gfn_write_track;
};

/*
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index 53c2adb25a07..42a4ae451d36 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -4,11 +4,6 @@

#include <linux/kvm_types.h>

-enum kvm_page_track_mode {
- KVM_PAGE_TRACK_WRITE,
- KVM_PAGE_TRACK_MAX,
-};
-
/*
* The notifier represented by @kvm_page_track_notifier_node is linked into
* the head which will be notified when guest is triggering the track event.
@@ -49,11 +44,9 @@ struct kvm_page_track_notifier_node {
};

void kvm_slot_page_track_add_page(struct kvm *kvm,
- struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode);
+ struct kvm_memory_slot *slot, gfn_t gfn);
void kvm_slot_page_track_remove_page(struct kvm *kvm,
- struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode);
+ struct kvm_memory_slot *slot, gfn_t gfn);

#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e192968340bf..7f21a1705438 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -820,8 +820,7 @@ static void account_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)

/* the non-leaf shadow pages are keeping readonly. */
if (sp->role.level > PG_LEVEL_4K)
- return kvm_slot_page_track_add_page(kvm, slot, gfn,
- KVM_PAGE_TRACK_WRITE);
+ return kvm_slot_page_track_add_page(kvm, slot, gfn);

kvm_mmu_gfn_disallow_lpage(slot, gfn);

@@ -867,8 +866,7 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
slots = kvm_memslots_for_spte_role(kvm, sp->role);
slot = __gfn_to_memslot(slots, gfn);
if (sp->role.level > PG_LEVEL_4K)
- return kvm_slot_page_track_remove_page(kvm, slot, gfn,
- KVM_PAGE_TRACK_WRITE);
+ return kvm_slot_page_track_remove_page(kvm, slot, gfn);

kvm_mmu_gfn_allow_lpage(slot, gfn);
}
@@ -2747,7 +2745,7 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot,
* track machinery is used to write-protect upper-level shadow pages,
* i.e. this guards the role.level == 4K assertion below!
*/
- if (kvm_slot_page_track_is_active(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE))
+ if (kvm_slot_page_track_is_active(kvm, slot, gfn))
return -EPERM;

/*
@@ -4155,7 +4153,7 @@ static bool page_fault_handle_page_track(struct kvm_vcpu *vcpu,
* guest is writing the page which is write tracked which can
* not be fixed by page fault handler.
*/
- if (kvm_slot_page_track_is_active(vcpu->kvm, fault->slot, fault->gfn, KVM_PAGE_TRACK_WRITE))
+ if (kvm_slot_page_track_is_active(vcpu->kvm, fault->slot, fault->gfn))
return true;

return false;
@@ -5387,8 +5385,8 @@ void kvm_mmu_after_set_cpuid(struct kvm_vcpu *vcpu)
* physical address properties) in a single VM would require tracking
* all relevant CPUID information in kvm_mmu_page_role. That is very
* undesirable as it would increase the memory requirements for
- * gfn_track (see struct kvm_mmu_page_role comments). For now that
- * problem is swept under the rug; KVM's CPUID API is horrific and
+ * gfn_write_track (see struct kvm_mmu_page_role comments). For now
+ * that problem is swept under the rug; KVM's CPUID API is horrific and
* it's all but impossible to solve it without introducing a new API.
*/
vcpu->arch.root_mmu.root_role.word = 0;
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 619ec8e5fd32..f8c89110f896 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -27,76 +27,50 @@ bool kvm_page_track_write_tracking_enabled(struct kvm *kvm)

void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
{
- int i;
+ kvfree(slot->arch.gfn_write_track);
+ slot->arch.gfn_write_track = NULL;
+}

- for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
- kvfree(slot->arch.gfn_track[i]);
- slot->arch.gfn_track[i] = NULL;
- }
+static int __kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot,
+ unsigned long npages)
+{
+ const size_t size = sizeof(*slot->arch.gfn_write_track);
+
+ if (!slot->arch.gfn_write_track)
+ slot->arch.gfn_write_track = __vcalloc(npages, size,
+ GFP_KERNEL_ACCOUNT);
+
+ return slot->arch.gfn_write_track ? 0 : -ENOMEM;
}

int kvm_page_track_create_memslot(struct kvm *kvm,
struct kvm_memory_slot *slot,
unsigned long npages)
{
- int i;
-
- for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
- if (i == KVM_PAGE_TRACK_WRITE &&
- !kvm_page_track_write_tracking_enabled(kvm))
- continue;
-
- slot->arch.gfn_track[i] =
- __vcalloc(npages, sizeof(*slot->arch.gfn_track[i]),
- GFP_KERNEL_ACCOUNT);
- if (!slot->arch.gfn_track[i])
- goto track_free;
- }
-
- return 0;
-
-track_free:
- kvm_page_track_free_memslot(slot);
- return -ENOMEM;
-}
-
-static inline bool page_track_mode_is_valid(enum kvm_page_track_mode mode)
-{
- if (mode < 0 || mode >= KVM_PAGE_TRACK_MAX)
- return false;
-
- return true;
-}
-
-int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot)
-{
- unsigned short *gfn_track;
-
- if (slot->arch.gfn_track[KVM_PAGE_TRACK_WRITE])
+ if (!kvm_page_track_write_tracking_enabled(kvm))
return 0;

- gfn_track = __vcalloc(slot->npages, sizeof(*gfn_track),
- GFP_KERNEL_ACCOUNT);
- if (gfn_track == NULL)
- return -ENOMEM;
+ return __kvm_page_track_write_tracking_alloc(slot, npages);
+}

- slot->arch.gfn_track[KVM_PAGE_TRACK_WRITE] = gfn_track;
- return 0;
+int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot)
+{
+ return __kvm_page_track_write_tracking_alloc(slot, slot->npages);
}

-static void update_gfn_track(struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode, short count)
+static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
+ short count)
{
int index, val;

index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);

- val = slot->arch.gfn_track[mode][index];
+ val = slot->arch.gfn_write_track[index];

if (WARN_ON(val + count < 0 || val + count > USHRT_MAX))
return;

- slot->arch.gfn_track[mode][index] += count;
+ slot->arch.gfn_write_track[index] += count;
}

/*
@@ -109,21 +83,15 @@ static void update_gfn_track(struct kvm_memory_slot *slot, gfn_t gfn,
* @kvm: the guest instance we are interested in.
* @slot: the @gfn belongs to.
* @gfn: the guest page.
- * @mode: tracking mode, currently only write track is supported.
*/
void kvm_slot_page_track_add_page(struct kvm *kvm,
- struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode)
+ struct kvm_memory_slot *slot, gfn_t gfn)
{

- if (WARN_ON(!page_track_mode_is_valid(mode)))
+ if (WARN_ON(!kvm_page_track_write_tracking_enabled(kvm)))
return;

- if (WARN_ON(mode == KVM_PAGE_TRACK_WRITE &&
- !kvm_page_track_write_tracking_enabled(kvm)))
- return;
-
- update_gfn_track(slot, gfn, mode, 1);
+ update_gfn_write_track(slot, gfn, 1);

/*
* new track stops large page mapping for the
@@ -131,9 +99,8 @@ void kvm_slot_page_track_add_page(struct kvm *kvm,
*/
kvm_mmu_gfn_disallow_lpage(slot, gfn);

- if (mode == KVM_PAGE_TRACK_WRITE)
- if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn, PG_LEVEL_4K))
- kvm_flush_remote_tlbs(kvm);
+ if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn, PG_LEVEL_4K))
+ kvm_flush_remote_tlbs(kvm);
}
EXPORT_SYMBOL_GPL(kvm_slot_page_track_add_page);

@@ -148,20 +115,14 @@ EXPORT_SYMBOL_GPL(kvm_slot_page_track_add_page);
* @kvm: the guest instance we are interested in.
* @slot: the @gfn belongs to.
* @gfn: the guest page.
- * @mode: tracking mode, currently only write track is supported.
*/
void kvm_slot_page_track_remove_page(struct kvm *kvm,
- struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode)
+ struct kvm_memory_slot *slot, gfn_t gfn)
{
- if (WARN_ON(!page_track_mode_is_valid(mode)))
+ if (WARN_ON(!kvm_page_track_write_tracking_enabled(kvm)))
return;

- if (WARN_ON(mode == KVM_PAGE_TRACK_WRITE &&
- !kvm_page_track_write_tracking_enabled(kvm)))
- return;
-
- update_gfn_track(slot, gfn, mode, -1);
+ update_gfn_write_track(slot, gfn, -1);

/*
* allow large page mapping for the tracked page
@@ -176,22 +137,18 @@ EXPORT_SYMBOL_GPL(kvm_slot_page_track_remove_page);
*/
bool kvm_slot_page_track_is_active(struct kvm *kvm,
const struct kvm_memory_slot *slot,
- gfn_t gfn, enum kvm_page_track_mode mode)
+ gfn_t gfn)
{
int index;

- if (WARN_ON(!page_track_mode_is_valid(mode)))
- return false;
-
if (!slot)
return false;

- if (mode == KVM_PAGE_TRACK_WRITE &&
- !kvm_page_track_write_tracking_enabled(kvm))
+ if (!kvm_page_track_write_tracking_enabled(kvm))
return false;

index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
- return !!READ_ONCE(slot->arch.gfn_track[mode][index]);
+ return !!READ_ONCE(slot->arch.gfn_write_track[index]);
}

#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
diff --git a/arch/x86/kvm/mmu/page_track.h b/arch/x86/kvm/mmu/page_track.h
index 931b26b8fc8f..789d0c479519 100644
--- a/arch/x86/kvm/mmu/page_track.h
+++ b/arch/x86/kvm/mmu/page_track.h
@@ -16,8 +16,7 @@ int kvm_page_track_create_memslot(struct kvm *kvm,
unsigned long npages);

bool kvm_slot_page_track_is_active(struct kvm *kvm,
- const struct kvm_memory_slot *slot,
- gfn_t gfn, enum kvm_page_track_mode mode);
+ const struct kvm_memory_slot *slot, gfn_t gfn);

#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
int kvm_page_track_init(struct kvm *kvm);
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 9f188b6c3edf..1e0f4ec55782 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -1578,7 +1578,7 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
}

write_lock(&kvm->mmu_lock);
- kvm_slot_page_track_add_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
+ kvm_slot_page_track_add_page(kvm, slot, gfn);
write_unlock(&kvm->mmu_lock);

srcu_read_unlock(&kvm->srcu, idx);
@@ -1607,7 +1607,7 @@ int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
}

write_lock(&kvm->mmu_lock);
- kvm_slot_page_track_remove_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
+ kvm_slot_page_track_remove_page(kvm, slot, gfn);
write_unlock(&kvm->mmu_lock);
srcu_read_unlock(&kvm->srcu, idx);

--
2.40.0.rc1.284.g88254d51c5-goog

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