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KVM: pfncache: remove KVM_GUEST_USES_PFN usage

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As noted in [1] the KVM_GUEST_USES_PFN usage flag is never set by any
callers of kvm_gpc_init(), and for good reason: the implementation is
incomplete/broken.  And it's not clear that there will ever be a user of
KVM_GUEST_USES_PFN, as coordinating vCPUs with mmu_notifier events is
non-trivial.

Remove KVM_GUEST_USES_PFN and all related code, e.g. dropping
KVM_GUEST_USES_PFN also makes the 'vcpu' argument redundant, to avoid
having to reason about broken code as __kvm_gpc_refresh() evolves.

Moreover, all existing callers specify KVM_HOST_USES_PFN so the usage
check in hva_to_pfn_retry() and hence the 'usage' argument to
kvm_gpc_init() are also redundant.

[1] https://lore.kernel.org/all/ZQiR8IpqOZrOpzHC@google.com

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-6-paul@xen.org
[sean: explicitly call out that guest usage is incomplete]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Paul Durrant 2024-02-15 15:29:00 +00:00 committed by Sean Christopherson
parent 78b74638eb
commit a4bff3df51
5 changed files with 15 additions and 79 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/kvm/x86.c
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@ -12056,7 +12056,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
vcpu->arch.regs_avail = ~0;
vcpu->arch.regs_dirty = ~0;
kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm, vcpu, KVM_HOST_USES_PFN);
kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm);
if (!irqchip_in_kernel(vcpu->kvm) || kvm_vcpu_is_reset_bsp(vcpu))
vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;

14
arch/x86/kvm/xen.c
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@ -2108,14 +2108,10 @@ void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
timer_setup(&vcpu->arch.xen.poll_timer, cancel_evtchn_poll, 0);
kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm, NULL,
KVM_HOST_USES_PFN);
kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm, NULL,
KVM_HOST_USES_PFN);
kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm, NULL,
KVM_HOST_USES_PFN);
kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm, NULL,
KVM_HOST_USES_PFN);
kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm);
kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm);
kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm);
kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm);
}
void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
@ -2158,7 +2154,7 @@ void kvm_xen_init_vm(struct kvm *kvm)
{
mutex_init(&kvm->arch.xen.xen_lock);
idr_init(&kvm->arch.xen.evtchn_ports);
kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm, NULL, KVM_HOST_USES_PFN);
kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm);
}
void kvm_xen_destroy_vm(struct kvm *kvm)

11
include/linux/kvm_host.h
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@ -1319,21 +1319,12 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
*
* @gpc: struct gfn_to_pfn_cache object.
* @kvm: pointer to kvm instance.
* @vcpu: vCPU to be used for marking pages dirty and to be woken on
* invalidation.
* @usage: indicates if the resulting host physical PFN is used while
* the @vcpu is IN_GUEST_MODE (in which case invalidation of
* the cache from MMU notifiers---but not for KVM memslot
* changes!---will also force @vcpu to exit the guest and
* refresh the cache); and/or if the PFN used directly
* by KVM (and thus needs a kernel virtual mapping).
*
* This sets up a gfn_to_pfn_cache by initializing locks and assigning the
* immutable attributes. Note, the cache must be zero-allocated (or zeroed by
* the caller before init).
*/
void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
struct kvm_vcpu *vcpu, enum pfn_cache_usage usage);
void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
/**
* kvm_gpc_activate - prepare a cached kernel mapping and HPA for a given guest

8
include/linux/kvm_types.h
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@ -49,12 +49,6 @@ typedef u64 hfn_t;
typedef hfn_t kvm_pfn_t;
enum pfn_cache_usage {
KVM_GUEST_USES_PFN = BIT(0),
KVM_HOST_USES_PFN = BIT(1),
KVM_GUEST_AND_HOST_USE_PFN = KVM_GUEST_USES_PFN | KVM_HOST_USES_PFN,
};
struct gfn_to_hva_cache {
u64 generation;
gpa_t gpa;
@ -69,13 +63,11 @@ struct gfn_to_pfn_cache {
unsigned long uhva;
struct kvm_memory_slot *memslot;
struct kvm *kvm;
struct kvm_vcpu *vcpu;
struct list_head list;
rwlock_t lock;
struct mutex refresh_lock;
void *khva;
kvm_pfn_t pfn;
enum pfn_cache_usage usage;
bool active;
bool valid;
};

59
virt/kvm/pfncache.c
View File

@ -25,9 +25,7 @@
void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
unsigned long end, bool may_block)
{
DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
struct gfn_to_pfn_cache *gpc;
bool evict_vcpus = false;
spin_lock(&kvm->gpc_lock);
list_for_each_entry(gpc, &kvm->gpc_list, list) {
@ -37,43 +35,10 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
gpc->uhva >= start && gpc->uhva < end) {
gpc->valid = false;
/*
* If a guest vCPU could be using the physical address,
* it needs to be forced out of guest mode.
*/
if (gpc->usage & KVM_GUEST_USES_PFN) {
if (!evict_vcpus) {
evict_vcpus = true;
bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
}
__set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap);
}
}
write_unlock_irq(&gpc->lock);
}
spin_unlock(&kvm->gpc_lock);
if (evict_vcpus) {
/*
* KVM needs to ensure the vCPU is fully out of guest context
* before allowing the invalidation to continue.
*/
unsigned int req = KVM_REQ_OUTSIDE_GUEST_MODE;
bool called;
/*
* If the OOM reaper is active, then all vCPUs should have
* been stopped already, so perform the request without
* KVM_REQUEST_WAIT and be sad if any needed to be IPI'd.
*/
if (!may_block)
req &= ~KVM_REQUEST_WAIT;
called = kvm_make_vcpus_request_mask(kvm, req, vcpu_bitmap);
WARN_ON_ONCE(called && !may_block);
}
}
bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
@ -206,16 +171,14 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
* pfn. Note, kmap() and memremap() can both sleep, so this
* too must be done outside of gpc->lock!
*/
if (gpc->usage & KVM_HOST_USES_PFN) {
if (new_pfn == gpc->pfn)
new_khva = old_khva;
else
new_khva = gpc_map(new_pfn);
if (new_pfn == gpc->pfn)
new_khva = old_khva;
else
new_khva = gpc_map(new_pfn);
if (!new_khva) {
kvm_release_pfn_clean(new_pfn);
goto out_error;
}
if (!new_khva) {
kvm_release_pfn_clean(new_pfn);
goto out_error;
}
write_lock_irq(&gpc->lock);
@ -346,18 +309,12 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
return __kvm_gpc_refresh(gpc, gpc->gpa, len);
}
void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
struct kvm_vcpu *vcpu, enum pfn_cache_usage usage)
void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
{
WARN_ON_ONCE(!usage || (usage & KVM_GUEST_AND_HOST_USE_PFN) != usage);
WARN_ON_ONCE((usage & KVM_GUEST_USES_PFN) && !vcpu);
rwlock_init(&gpc->lock);
mutex_init(&gpc->refresh_lock);
gpc->kvm = kvm;
gpc->vcpu = vcpu;
gpc->usage = usage;
gpc->pfn = KVM_PFN_ERR_FAULT;
gpc->uhva = KVM_HVA_ERR_BAD;
}