[PATCH v4 07/13] KVM: xen: prepare for using 'default' vcpu_info

From: Paul Durrant
Date: Tue Sep 19 2023 - 09:42:31 EST

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From: Paul Durrant <pdurrant@xxxxxxxxxx>

The shared_info page contains an array of 32 vcpu_info structures
which may be used by guests (with fewer than 32 vCPUs) if they don't
explicitly register vcpu_info structures in their own memory, using
a VCPUOP_register_vcpu_info hypercall.
Currently we rely on the VMM always registering vcpu_info structures,
even if the guest doesn't make that hypercall, which is somewhat
bogus as (as has been stated in the comment of a previous commit)
the shared_info page is not guest memory.
Prepare to automatically use the vcpu_info info embedded in shared_info
by default, by adding a get_vcpu_info_cache() helper function. This
function also passes back an offset to be added to the cached khva.
This is currently always zero since we're still relying on the
current VMM behaviour. A subsequent patch will make proper use of
it.

No functional change intended.

NOTE: To avoid leaking detail of the vcpu_info duality into the main
x86 code, a kvm_xen_guest_time_update() has also been added
and use of this requires that kvm_setup_guest_pvclock() ceases
to be a static function.

Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx

v4:
- Added missing offset into calls to kvm_gpc_check() and
kvm_gpc_refresh().

v2:
- Fix build warning.
---
arch/x86/include/asm/kvm_host.h | 4 +++
arch/x86/kvm/x86.c | 12 +++----
arch/x86/kvm/xen.c | 60 ++++++++++++++++++++++++---------
arch/x86/kvm/xen.h | 6 +++-
4 files changed, 58 insertions(+), 24 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1a4def36d5bb..6d896f9161c2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2238,4 +2238,8 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
*/
#define KVM_EXIT_HYPERCALL_MBZ GENMASK_ULL(31, 1)

+void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
+ struct gfn_to_pfn_cache *gpc,
+ unsigned int offset);
+
#endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d669a8801265..2d7d0ae18820 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3094,9 +3094,9 @@ u64 get_kvmclock_ns(struct kvm *kvm)
return data.clock;
}

-static void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
- struct gfn_to_pfn_cache *gpc,
- unsigned int offset)
+void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
+ struct gfn_to_pfn_cache *gpc,
+ unsigned int offset)
{
struct kvm_vcpu_arch *vcpu = &v->arch;
struct pvclock_vcpu_time_info *guest_hv_clock;
@@ -3232,11 +3232,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)

if (vcpu->pv_time.active)
kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0);
- if (vcpu->xen.vcpu_info_cache.active)
- kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache,
- offsetof(struct compat_vcpu_info, time));
- if (vcpu->xen.vcpu_time_info_cache.active)
- kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0);
+ kvm_xen_guest_time_update(v);
kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
return 0;
}
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 1abb4547642a..9449cfe1048f 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -489,6 +489,29 @@ static void kvm_xen_inject_vcpu_vector(struct kvm_vcpu *v)
WARN_ON_ONCE(!kvm_irq_delivery_to_apic_fast(v->kvm, NULL, &irq, &r, NULL));
}

+static struct gfn_to_pfn_cache *get_vcpu_info_cache(struct kvm_vcpu *v, unsigned long *offset)
+{
+ if (offset)
+ *offset = 0;
+
+ return &v->arch.xen.vcpu_info_cache;
+}
+
+void kvm_xen_guest_time_update(struct kvm_vcpu *v)
+{
+ unsigned long offset;
+ struct gfn_to_pfn_cache *gpc = get_vcpu_info_cache(v, &offset);
+
+ BUILD_BUG_ON(offsetof(struct vcpu_info, time) !=
+ offsetof(struct compat_vcpu_info, time));
+
+ if (gpc->active)
+ kvm_setup_guest_pvclock(v, gpc, offset + offsetof(struct compat_vcpu_info, time));
+
+ if (v->arch.xen.vcpu_time_info_cache.active)
+ kvm_setup_guest_pvclock(v, &v->arch.xen.vcpu_time_info_cache, 0);
+}
+
/*
* On event channel delivery, the vcpu_info may not have been accessible.
* In that case, there are bits in vcpu->arch.xen.evtchn_pending_sel which
@@ -499,7 +522,8 @@ static void kvm_xen_inject_vcpu_vector(struct kvm_vcpu *v)
void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
{
unsigned long evtchn_pending_sel = READ_ONCE(v->arch.xen.evtchn_pending_sel);
- struct gfn_to_pfn_cache *gpc = &v->arch.xen.vcpu_info_cache;
+ unsigned long offset;
+ struct gfn_to_pfn_cache *gpc = get_vcpu_info_cache(v, &offset);
unsigned long flags;

if (!evtchn_pending_sel)
@@ -511,10 +535,10 @@ 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, sizeof(struct vcpu_info))) {
+ while (!kvm_gpc_check(gpc, offset + sizeof(struct vcpu_info))) {
read_unlock_irqrestore(&gpc->lock, flags);

- if (kvm_gpc_refresh(gpc, sizeof(struct vcpu_info)))
+ if (kvm_gpc_refresh(gpc, offset + sizeof(struct vcpu_info)))
return;

read_lock_irqsave(&gpc->lock, flags);
@@ -522,7 +546,7 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)

/* Now gpc->khva is a valid kernel address for the vcpu_info */
if (IS_ENABLED(CONFIG_64BIT) && v->kvm->arch.xen.long_mode) {
- struct vcpu_info *vi = gpc->khva;
+ struct vcpu_info *vi = gpc->khva + offset;

asm volatile(LOCK_PREFIX "orq %0, %1\n"
"notq %0\n"
@@ -534,7 +558,7 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
WRITE_ONCE(vi->evtchn_upcall_pending, 1);
} else {
u32 evtchn_pending_sel32 = evtchn_pending_sel;
- struct compat_vcpu_info *vi = gpc->khva;
+ struct compat_vcpu_info *vi = gpc->khva + offset;

asm volatile(LOCK_PREFIX "orl %0, %1\n"
"notl %0\n"
@@ -556,7 +580,8 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)

int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
{
- struct gfn_to_pfn_cache *gpc = &v->arch.xen.vcpu_info_cache;
+ unsigned long offset;
+ struct gfn_to_pfn_cache *gpc = get_vcpu_info_cache(v, &offset);
unsigned long flags;
u8 rc = 0;

@@ -574,7 +599,7 @@ 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, sizeof(struct vcpu_info))) {
+ while (!kvm_gpc_check(gpc, offset + sizeof(struct vcpu_info))) {
read_unlock_irqrestore(&gpc->lock, flags);

/*
@@ -588,7 +613,7 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
if (in_atomic() || !task_is_running(current))
return 1;

- if (kvm_gpc_refresh(gpc, sizeof(struct vcpu_info))) {
+ if (kvm_gpc_refresh(gpc, offset + sizeof(struct vcpu_info))) {
/*
* If this failed, userspace has screwed up the
* vcpu_info mapping. No interrupts for you.
@@ -598,7 +623,7 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
read_lock_irqsave(&gpc->lock, flags);
}

- rc = ((struct vcpu_info *)gpc->khva)->evtchn_upcall_pending;
+ rc = ((struct vcpu_info *)(gpc->khva + offset))->evtchn_upcall_pending;
read_unlock_irqrestore(&gpc->lock, flags);
return rc;
}
@@ -1567,7 +1592,7 @@ static void kvm_xen_check_poller(struct kvm_vcpu *vcpu, int port)
*/
int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
{
- struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
+ struct gfn_to_pfn_cache *gpc;
struct kvm_vcpu *vcpu;
unsigned long *pending_bits, *mask_bits;
unsigned long flags;
@@ -1585,7 +1610,8 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
WRITE_ONCE(xe->vcpu_idx, vcpu->vcpu_idx);
}

- if (!vcpu->arch.xen.vcpu_info_cache.active)
+ gpc = get_vcpu_info_cache(vcpu, NULL);
+ if (!gpc->active)
return -EINVAL;

if (xe->port >= max_evtchn_port(kvm))
@@ -1594,6 +1620,7 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
rc = -EWOULDBLOCK;

idx = srcu_read_lock(&kvm->srcu);
+ gpc = &kvm->arch.xen.shinfo_cache;

read_lock_irqsave(&gpc->lock, flags);
if (!kvm_gpc_check(gpc, PAGE_SIZE))
@@ -1624,13 +1651,16 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
rc = -ENOTCONN; /* Masked */
kvm_xen_check_poller(vcpu, xe->port);
} else {
+ unsigned long offset;
+
rc = 1; /* Delivered to the bitmap in shared_info. */
+
/* Now switch to the vCPU's vcpu_info to set the index and pending_sel */
read_unlock_irqrestore(&gpc->lock, flags);
- gpc = &vcpu->arch.xen.vcpu_info_cache;
+ gpc = get_vcpu_info_cache(vcpu, &offset);

read_lock_irqsave(&gpc->lock, flags);
- if (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) {
+ if (!kvm_gpc_check(gpc, offset + sizeof(struct vcpu_info))) {
/*
* Could not access the vcpu_info. Set the bit in-kernel
* and prod the vCPU to deliver it for itself.
@@ -1641,13 +1671,13 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
}

if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
- struct vcpu_info *vcpu_info = gpc->khva;
+ struct vcpu_info *vcpu_info = gpc->khva + offset;
if (!test_and_set_bit(port_word_bit, &vcpu_info->evtchn_pending_sel)) {
WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
kick_vcpu = true;
}
} else {
- struct compat_vcpu_info *vcpu_info = gpc->khva;
+ struct compat_vcpu_info *vcpu_info = gpc->khva + offset;
if (!test_and_set_bit(port_word_bit,
(unsigned long *)&vcpu_info->evtchn_pending_sel)) {
WRITE_ONCE(vcpu_info->evtchn_upcall_pending, 1);
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index f8f1fe22d090..c4d29ccbc3ab 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -16,6 +16,7 @@

extern struct static_key_false_deferred kvm_xen_enabled;

+void kvm_xen_guest_time_update(struct kvm_vcpu *vcpu);
int __kvm_xen_has_interrupt(struct kvm_vcpu *vcpu);
void kvm_xen_inject_pending_events(struct kvm_vcpu *vcpu);
int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
@@ -52,7 +53,6 @@ static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
{
if (static_branch_unlikely(&kvm_xen_enabled.key) &&
- vcpu->arch.xen.vcpu_info_cache.active &&
vcpu->kvm->arch.xen.upcall_vector)
return __kvm_xen_has_interrupt(vcpu);

@@ -80,6 +80,10 @@ static inline int kvm_xen_has_pending_timer(struct kvm_vcpu *vcpu)

void kvm_xen_inject_timer_irqs(struct kvm_vcpu *vcpu);
#else
+static inline void kvm_xen_guest_time_update(struct kvm_vcpu *vcpu)
+{
+}
+
static inline int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
{
return 1;
--
2.39.2

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