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KVM: x86/mmu: Drop infrastructure for multiple page-track modes

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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@google.com
Cc: Ben Gardon <bgardon@google.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Link: https://lore.kernel.org/r/20230729013535.1070024-24-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2023-07-28 18:35:29 -07:00
committed by Paolo Bonzini
parent e998fb1a30
commit 338068b5be
6 changed files with 49 additions and 103 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/include/asm/kvm_host.h
View File

@@ -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;
};
/*

11
arch/x86/include/asm/kvm_page_track.h
View File

@@ -4,17 +4,10 @@
#include <linux/kvm_types.h>
enum kvm_page_track_mode {
KVM_PAGE_TRACK_WRITE,
KVM_PAGE_TRACK_MAX,
};
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
/*

14
arch/x86/kvm/mmu/mmu.c
View File

@@ -831,8 +831,7 @@ 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);
@@ -878,8 +877,7 @@ 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);
}
@@ -2809,7 +2807,7 @@ 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;
/*
@@ -4203,7 +4201,7 @@ 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;
@@ -5422,8 +5420,8 @@ 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;

108
arch/x86/kvm/mmu/page_track.c
View File

@@ -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;
if (!kvm_page_track_write_tracking_enabled(kvm))
return 0;
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;
return __kvm_page_track_write_tracking_alloc(slot, npages);
}
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])
return 0;
gfn_track = __vcalloc(slot->npages, sizeof(*gfn_track),
GFP_KERNEL_ACCOUNT);
if (gfn_track == NULL)
return -ENOMEM;
slot->arch.gfn_track[KVM_PAGE_TRACK_WRITE] = gfn_track;
return 0;
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_ONCE(val + count < 0 || val + count > USHRT_MAX))
return;
slot->arch.gfn_track[mode][index] += count;
slot->arch.gfn_write_track[index] += count;
}
/*
@@ -109,21 +83,14 @@ 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_ONCE(!page_track_mode_is_valid(mode)))
if (WARN_ON_ONCE(!kvm_page_track_write_tracking_enabled(kvm)))
return;
if (WARN_ON_ONCE(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 +98,8 @@ 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 +114,14 @@ 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_ONCE(!page_track_mode_is_valid(mode)))
if (WARN_ON_ONCE(!kvm_page_track_write_tracking_enabled(kvm)))
return;
if (WARN_ON_ONCE(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 +136,18 @@ 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_ONCE(!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

3
arch/x86/kvm/mmu/page_track.h
View File

@@ -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);

4
drivers/gpu/drm/i915/gvt/kvmgt.c
View File

@@ -1564,7 +1564,7 @@ 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);
@@ -1593,7 +1593,7 @@ 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);