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KVM: Drop @gpa from exported gfn=>pfn cache check() and refresh() hel…
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…pers

Drop the @gpa param from the exported check()+refresh() helpers and limit
changing the cache's GPA to the activate path.  All external users just
feed in gpc->gpa, i.e. this is a fancy nop.

Allowing users to change the GPA at check()+refresh() is dangerous as
those helpers explicitly allow concurrent calls, e.g. KVM could get into
a livelock scenario.  It's also unclear as to what the expected behavior
should be if multiple tasks attempt to refresh with different GPAs.

Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: David Woodhouse <[email protected]>
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@sean-jc @dwmw2
sean-jc authored and dwmw2 committed Nov 30, 2022
1 parent 5762cb1 commit 58f5ee5
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Showing 4 changed files with 27 additions and 26 deletions.
6 changes: 2 additions & 4 deletions arch/x86/kvm/x86.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3035,12 +3035,10 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
unsigned long flags;

read_lock_irqsave(&gpc->lock, flags);
while (!kvm_gpc_check(gpc, gpc->gpa,
offset + sizeof(*guest_hv_clock))) {
while (!kvm_gpc_check(gpc, offset + sizeof(*guest_hv_clock))) {
read_unlock_irqrestore(&gpc->lock, flags);

if (kvm_gpc_refresh(gpc, gpc->gpa,
offset + sizeof(*guest_hv_clock)))
if (kvm_gpc_refresh(gpc, offset + sizeof(*guest_hv_clock)))
return;

read_lock_irqsave(&gpc->lock, flags);
Expand Down
22 changes: 11 additions & 11 deletions arch/x86/kvm/xen.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -272,14 +272,14 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
* gfn_to_pfn caches that cover the region.
*/
read_lock_irqsave(&gpc1->lock, flags);
while (!kvm_gpc_check(gpc1, gpc1->gpa, user_len1)) {
while (!kvm_gpc_check(gpc1, user_len1)) {
read_unlock_irqrestore(&gpc1->lock, flags);

/* When invoked from kvm_sched_out() we cannot sleep */
if (atomic)
return;

if (kvm_gpc_refresh(gpc1, gpc1->gpa, user_len1))
if (kvm_gpc_refresh(gpc1, user_len1))
return;

read_lock_irqsave(&gpc1->lock, flags);
Expand Down Expand Up @@ -308,7 +308,7 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
*/
read_lock(&gpc2->lock);

if (!kvm_gpc_check(gpc2, gpc2->gpa, user_len2)) {
if (!kvm_gpc_check(gpc2, user_len2)) {
read_unlock(&gpc2->lock);
read_unlock_irqrestore(&gpc1->lock, flags);

Expand Down Expand Up @@ -488,10 +488,10 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
* little more honest about it.
*/
read_lock_irqsave(&gpc->lock, flags);
while (!kvm_gpc_check(gpc, gpc->gpa, sizeof(struct vcpu_info))) {
while (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) {
read_unlock_irqrestore(&gpc->lock, flags);

if (kvm_gpc_refresh(gpc, gpc->gpa, sizeof(struct vcpu_info)))
if (kvm_gpc_refresh(gpc, sizeof(struct vcpu_info)))
return;

read_lock_irqsave(&gpc->lock, flags);
Expand Down Expand Up @@ -551,7 +551,7 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
sizeof_field(struct compat_vcpu_info, evtchn_upcall_pending));

read_lock_irqsave(&gpc->lock, flags);
while (!kvm_gpc_check(gpc, gpc->gpa, sizeof(struct vcpu_info))) {
while (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) {
read_unlock_irqrestore(&gpc->lock, flags);

/*
Expand All @@ -565,7 +565,7 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
if (in_atomic() || !task_is_running(current))
return 1;

if (kvm_gpc_refresh(gpc, gpc->gpa, sizeof(struct vcpu_info))) {
if (kvm_gpc_refresh(gpc, sizeof(struct vcpu_info))) {
/*
* If this failed, userspace has screwed up the
* vcpu_info mapping. No interrupts for you.
Expand Down Expand Up @@ -1154,7 +1154,7 @@ static bool wait_pending_event(struct kvm_vcpu *vcpu, int nr_ports,

read_lock_irqsave(&gpc->lock, flags);
idx = srcu_read_lock(&kvm->srcu);
if (!kvm_gpc_check(gpc, gpc->gpa, PAGE_SIZE))
if (!kvm_gpc_check(gpc, PAGE_SIZE))
goto out_rcu;

ret = false;
Expand Down Expand Up @@ -1576,7 +1576,7 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
idx = srcu_read_lock(&kvm->srcu);

read_lock_irqsave(&gpc->lock, flags);
if (!kvm_gpc_check(gpc, gpc->gpa, PAGE_SIZE))
if (!kvm_gpc_check(gpc, PAGE_SIZE))
goto out_rcu;

if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
Expand Down Expand Up @@ -1610,7 +1610,7 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
gpc = &vcpu->arch.xen.vcpu_info_cache;

read_lock_irqsave(&gpc->lock, flags);
if (!kvm_gpc_check(gpc, gpc->gpa, sizeof(struct vcpu_info))) {
if (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) {
/*
* Could not access the vcpu_info. Set the bit in-kernel
* and prod the vCPU to deliver it for itself.
Expand Down Expand Up @@ -1708,7 +1708,7 @@ static int kvm_xen_set_evtchn(struct kvm_xen_evtchn *xe, struct kvm *kvm)
break;

idx = srcu_read_lock(&kvm->srcu);
rc = kvm_gpc_refresh(gpc, gpc->gpa, PAGE_SIZE);
rc = kvm_gpc_refresh(gpc, PAGE_SIZE);
srcu_read_unlock(&kvm->srcu, idx);
} while(!rc);

Expand Down
8 changes: 3 additions & 5 deletions include/linux/kvm_host.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1299,7 +1299,6 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
* kvm_gpc_check - check validity of a gfn_to_pfn_cache.
*
* @gpc: struct gfn_to_pfn_cache object.
* @gpa: current guest physical address to map.
* @len: sanity check; the range being access must fit a single page.
*
* @return: %true if the cache is still valid and the address matches.
Expand All @@ -1312,15 +1311,14 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
* Callers in IN_GUEST_MODE may do so without locking, although they should
* still hold a read lock on kvm->scru for the memslot checks.
*/
bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);
bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len);

/**
* kvm_gpc_refresh - update a previously initialized cache.
*
* @gpc: struct gfn_to_pfn_cache object.
* @gpa: updated guest physical address to map.
* @len: sanity check; the range being access must fit a single page.
*
* @return: 0 for success.
* -EINVAL for a mapping which would cross a page boundary.
* -EFAULT for an untranslatable guest physical address.
Expand All @@ -1331,7 +1329,7 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);
* still lock and check the cache status, as this function does not return
* with the lock still held to permit access.
*/
int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);
int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len);

/**
* kvm_gpc_deactivate - deactivate and unlink a gfn_to_pfn_cache.
Expand Down
17 changes: 11 additions & 6 deletions virt/kvm/pfncache.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -76,18 +76,17 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
}
}

bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
{
struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

if (!gpc->active)
return false;

if ((gpa & ~PAGE_MASK) + len > PAGE_SIZE)
if ((gpc->gpa & ~PAGE_MASK) + len > PAGE_SIZE)
return false;

if (gpc->gpa != gpa || gpc->generation != slots->generation ||
kvm_is_error_hva(gpc->uhva))
if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
return false;

if (!gpc->valid)
Expand Down Expand Up @@ -237,7 +236,8 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
return -EFAULT;
}

int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
unsigned long len)
{
struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
unsigned long page_offset = gpa & ~PAGE_MASK;
Expand Down Expand Up @@ -331,6 +331,11 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)

return ret;
}

int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
{
return __kvm_gpc_refresh(gpc, gpc->gpa, len);
}
EXPORT_SYMBOL_GPL(kvm_gpc_refresh);

void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
Expand Down Expand Up @@ -371,7 +376,7 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
gpc->active = true;
write_unlock_irq(&gpc->lock);
}
return kvm_gpc_refresh(gpc, gpa, len);
return __kvm_gpc_refresh(gpc, gpa, len);
}
EXPORT_SYMBOL_GPL(kvm_gpc_activate);

Expand Down

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