[PATCH 13/16] KVM: Drop @gpa from exported gfn=>pfn cache check() and refresh() helpers

From: Paolo Bonzini
Date: Thu Oct 27 2022 - 12:20:20 EST

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From: Sean Christopherson <seanjc@xxxxxxxxxx>

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 <seanjc@xxxxxxxxxx>
Message-Id: <20221013211234.1318131-14-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 4 ++--
arch/x86/kvm/xen.c | 20 ++++++++++----------
include/linux/kvm_host.h | 6 ++----
virt/kvm/pfncache.c | 11 ++++-------
4 files changed, 18 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bdc3110650d3..f7ee5ee58990 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3034,10 +3034,10 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
WARN_ON_ONCE(gpc->len != offset + sizeof(*guest_hv_clock));

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

- if (kvm_gpc_refresh(gpc, gpc->gpa))
+ if (kvm_gpc_refresh(gpc))
return;

read_lock_irqsave(&gpc->lock, flags);
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 545ecbd0ca36..7b7b1eb88a0b 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -241,14 +241,14 @@ void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, int state)
return;

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

/* When invoked from kvm_sched_out() we cannot sleep */
if (state == RUNSTATE_runnable)
return;

- if (kvm_gpc_refresh(gpc, gpc->gpa))
+ if (kvm_gpc_refresh(gpc))
return;

read_lock_irqsave(&gpc->lock, flags);
@@ -374,10 +374,10 @@ 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)) {
+ while (!kvm_gpc_check(gpc)) {
read_unlock_irqrestore(&gpc->lock, flags);

- if (kvm_gpc_refresh(gpc, gpc->gpa))
+ if (kvm_gpc_refresh(gpc))
return;

read_lock_irqsave(&gpc->lock, flags);
@@ -437,7 +437,7 @@ 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)) {
+ while (!kvm_gpc_check(gpc)) {
read_unlock_irqrestore(&gpc->lock, flags);

/*
@@ -451,7 +451,7 @@ 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)) {
+ if (kvm_gpc_refresh(gpc)) {
/*
* If this failed, userspace has screwed up the
* vcpu_info mapping. No interrupts for you.
@@ -981,7 +981,7 @@ 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))
+ if (!kvm_gpc_check(gpc))
goto out_rcu;

ret = false;
@@ -1372,7 +1372,7 @@ 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))
+ if (!kvm_gpc_check(gpc))
goto out_rcu;

if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
@@ -1406,7 +1406,7 @@ 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)) {
+ if (!kvm_gpc_check(gpc)) {
/*
* Could not access the vcpu_info. Set the bit in-kernel
* and prod the vCPU to deliver it for itself.
@@ -1504,7 +1504,7 @@ 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);
+ rc = kvm_gpc_refresh(gpc);
srcu_read_unlock(&kvm->srcu, idx);
} while(!rc);

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3847b721e753..fd6b58c870cf 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1282,7 +1282,6 @@ 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.
*
* @return: %true if the cache is still valid and the address matches.
* %false if the cache is not valid.
@@ -1294,13 +1293,12 @@ 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);
+bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc);

/**
* kvm_gpc_refresh - update a previously initialized cache.
*
* @gpc: struct gfn_to_pfn_cache object.
- * @gpa: updated guest physical address to map.
*
* @return: 0 for success.
* -EINVAL for a mapping which would cross a page boundary.
@@ -1312,7 +1310,7 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, gpa_t gpa);
* 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);
+int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc);

/**
* kvm_gpc_deactivate - deactivate and unlink a gfn_to_pfn_cache.
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 06fcf03c2da6..68e2e53eac8a 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -76,17 +76,14 @@ 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)
+bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc)
{
struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

if (!gpc->active)
return false;

- if ((gpa & ~PAGE_MASK) + gpc->len > PAGE_SIZE)
- return false;
-
- if (gpc->gpa != gpa || gpc->generation != slots->generation ||
+ if (gpc->generation != slots->generation ||
kvm_is_error_hva(gpc->uhva))
return false;

@@ -329,9 +326,9 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned l
return ret;
}

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

--
2.31.1

Next message: Paolo Bonzini: "[PATCH 16/16] KVM: selftests: Mark "guest_saw_irq" as volatile in xen_shinfo_test"
Previous message: Paolo Bonzini: "[PATCH 04/16] KVM: Shorten gfn_to_pfn_cache function names"
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Next in thread: Paolo Bonzini: "[PATCH 16/16] KVM: selftests: Mark "guest_saw_irq" as volatile in xen_shinfo_test"
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