diff mbox series

[v8,08/15] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

Message ID 20231121180223.12484-9-paul@xen.org (mailing list archive)
State New, archived
Headers show
Series KVM: xen: update shared_info and vcpu_info handling | expand

Commit Message

Paul Durrant Nov. 21, 2023, 6:02 p.m. UTC 
From: Paul Durrant <pdurrant@amazon.com>

Some pfncache pages may actually be overlays on guest memory that have a
fixed HVA within the VMM. It's pointless to invalidate such cached
mappings if the overlay is moved so allow a cache to be activated directly
with the HVA to cater for such cases. A subsequent patch will make use
of this facility.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v8:
 - Re-worked to avoid messing with struct gfn_to_pfn_cache.
---
 include/linux/kvm_host.h | 19 +++++++++++++++++-
 virt/kvm/pfncache.c      | 43 ++++++++++++++++++++++++++++++----------
 2 files changed, 51 insertions(+), 11 deletions(-)

Comments

David Woodhouse Nov. 21, 2023, 10:47 p.m. UTC | #1 
On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
> 
> -static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> +static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, u64 addr, bool addr_is_gpa,
>                              unsigned long len)
>  {
>         struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
> -       unsigned long page_offset = offset_in_page(gpa);
> +       unsigned long page_offset = offset_in_page(addr);
>         bool unmap_old = false;
>         kvm_pfn_t old_pfn;
>         bool hva_change = false;
> @@ -244,12 +244,21 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>         old_pfn = gpc->pfn;
>         old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
>  
> -       /* If the userspace HVA is invalid, refresh that first */
> -       if (gpc->gpa != gpa || gpc->generation != slots->generation ||
> -           kvm_is_error_hva(gpc->uhva)) {
> -               gfn_t gfn = gpa_to_gfn(gpa);
> +       if (!addr_is_gpa) {
> +               gpc->gpa = KVM_XEN_INVALID_GPA;
> +               gpc->uhva = PAGE_ALIGN_DOWN(gpc->uhva);
> +               addr = PAGE_ALIGN_DOWN(addr);
> +
> +               if (gpc->uhva != addr) {
> +                       gpc->uhva = addr;
> +                       hva_change = true;
> +               }
> +       } else if (gpc->gpa != addr ||
> +                  gpc->generation != slots->generation ||
> +                  kvm_is_error_hva(gpc->uhva)) {
> +               gfn_t gfn = gpa_to_gfn(addr);
>  
> -               gpc->gpa = gpa;
> +               gpc->gpa = addr;
>                 gpc->generation = slots->generation;
>                 gpc->memslot = __gfn_to_memslot(slots, gfn);
>                 gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);

Hrm, now that a previous patch means we're preserving the low bits of
gpc->uhva surely you don't *need* to mess with the gpc struct? 

If gpc->gpa == KVM_XEN_INVALID_GPA (but gpc->uhva != KVM_ERR_ERR_BAD &&
gpc->active) surely that's enough to signal that gpc->uhva is canonical
and doesn't need to be looked up from the GPA?

And I think that means the 'bool addr_is_gpa' argument can go away from
__kvm_gpc_refresh(); you can set it up in {__,}kvm_gpc_activate*()
instead?
Paul Durrant Nov. 22, 2023, 10:07 a.m. UTC | #2 
On 21/11/2023 22:47, David Woodhouse wrote:
> On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
>>
>> -static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>> +static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, u64 addr, bool addr_is_gpa,
>>                               unsigned long len)
>>   {
>>          struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
>> -       unsigned long page_offset = offset_in_page(gpa);
>> +       unsigned long page_offset = offset_in_page(addr);
>>          bool unmap_old = false;
>>          kvm_pfn_t old_pfn;
>>          bool hva_change = false;
>> @@ -244,12 +244,21 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>>          old_pfn = gpc->pfn;
>>          old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
>>   
>> -       /* If the userspace HVA is invalid, refresh that first */
>> -       if (gpc->gpa != gpa || gpc->generation != slots->generation ||
>> -           kvm_is_error_hva(gpc->uhva)) {
>> -               gfn_t gfn = gpa_to_gfn(gpa);
>> +       if (!addr_is_gpa) {
>> +               gpc->gpa = KVM_XEN_INVALID_GPA;
>> +               gpc->uhva = PAGE_ALIGN_DOWN(gpc->uhva);
>> +               addr = PAGE_ALIGN_DOWN(addr);
>> +
>> +               if (gpc->uhva != addr) {
>> +                       gpc->uhva = addr;
>> +                       hva_change = true;
>> +               }
>> +       } else if (gpc->gpa != addr ||
>> +                  gpc->generation != slots->generation ||
>> +                  kvm_is_error_hva(gpc->uhva)) {
>> +               gfn_t gfn = gpa_to_gfn(addr);
>>   
>> -               gpc->gpa = gpa;
>> +               gpc->gpa = addr;
>>                  gpc->generation = slots->generation;
>>                  gpc->memslot = __gfn_to_memslot(slots, gfn);
>>                  gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);
> 
> Hrm, now that a previous patch means we're preserving the low bits of
> gpc->uhva surely you don't *need* to mess with the gpc struct?
> 

I'm not messing with it, am I?

> If gpc->gpa == KVM_XEN_INVALID_GPA (but gpc->uhva != KVM_ERR_ERR_BAD &&
> gpc->active) surely that's enough to signal that gpc->uhva is canonical
> and doesn't need to be looked up from the GPA?
> 
> And I think that means the 'bool addr_is_gpa' argument can go away from
> __kvm_gpc_refresh(); you can set it up in {__,}kvm_gpc_activate*()
> instead?

Alas not... __kvm_gpc_refresh() still needs to know *something* has 
changed, otherwise the khva will be stale.

   Paul
diff mbox series

Patch

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b1dc2e5a64f3..484c587e8290 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1312,6 +1312,22 @@  void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
  */
 int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);
 
+/**
+ * kvm_gpc_activate_hva - prepare a cached kernel mapping and HPA for a given HVA.
+ *
+ * @gpc:          struct gfn_to_pfn_cache object.
+ * @hva:          userspace virtual 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.
+ *
+ * The semantics of this function are the same as those of kvm_gpc_activate(). It
+ * merely bypasses a layer of address translation.
+ */
+int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long hva, unsigned long len);
+
 /**
  * kvm_gpc_check - check validity of a gfn_to_pfn_cache.
  *
@@ -1365,7 +1381,8 @@  void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
  */
 static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
 {
-	mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
+	if (gpc->gpa != KVM_XEN_INVALID_GPA)
+		mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 }
 
 void kvm_sigset_activate(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index c545f6246501..ed700afeec49 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -209,11 +209,11 @@  static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 	return -EFAULT;
 }
 
-static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
+static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, u64 addr, bool addr_is_gpa,
 			     unsigned long len)
 {
 	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
-	unsigned long page_offset = offset_in_page(gpa);
+	unsigned long page_offset = offset_in_page(addr);
 	bool unmap_old = false;
 	kvm_pfn_t old_pfn;
 	bool hva_change = false;
@@ -244,12 +244,21 @@  static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	old_pfn = gpc->pfn;
 	old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 
-	/* If the userspace HVA is invalid, refresh that first */
-	if (gpc->gpa != gpa || gpc->generation != slots->generation ||
-	    kvm_is_error_hva(gpc->uhva)) {
-		gfn_t gfn = gpa_to_gfn(gpa);
+	if (!addr_is_gpa) {
+		gpc->gpa = KVM_XEN_INVALID_GPA;
+		gpc->uhva = PAGE_ALIGN_DOWN(gpc->uhva);
+		addr = PAGE_ALIGN_DOWN(addr);
+
+		if (gpc->uhva != addr) {
+			gpc->uhva = addr;
+			hva_change = true;
+		}
+	} else if (gpc->gpa != addr ||
+		   gpc->generation != slots->generation ||
+		   kvm_is_error_hva(gpc->uhva)) {
+		gfn_t gfn = gpa_to_gfn(addr);
 
-		gpc->gpa = gpa;
+		gpc->gpa = addr;
 		gpc->generation = slots->generation;
 		gpc->memslot = __gfn_to_memslot(slots, gfn);
 		gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);
@@ -317,7 +326,10 @@  static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 
 int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
 {
-	return __kvm_gpc_refresh(gpc, gpc->gpa, len);
+	if (gpc->gpa != KVM_XEN_INVALID_GPA)
+		return __kvm_gpc_refresh(gpc, gpc->gpa, true, len);
+
+	return __kvm_gpc_refresh(gpc, gpc->uhva, false, len);
 }
 
 void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
@@ -330,7 +342,8 @@  void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
 	gpc->uhva = KVM_HVA_ERR_BAD;
 }
 
-int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
+static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, u64 addr, bool addr_is_gpa,
+			      unsigned long len)
 {
 	struct kvm *kvm = gpc->kvm;
 
@@ -351,7 +364,17 @@  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, addr, addr_is_gpa, len);
+}
+
+int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
+{
+	return __kvm_gpc_activate(gpc, gpa, true, len);
+}
+
+int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long hva, unsigned long len)
+{
+	return __kvm_gpc_activate(gpc, hva, false, len);
 }
 
 void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)