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From:   Paul Durrant <paul@xen.org>
To:     David Woodhouse <dwmw2@infradead.org>, Paul Durrant <paul@xen.org>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v9 08/15] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA
Date:   Wed, 22 Nov 2023 12:18:15 +0000
Message-Id: <20231122121822.1042-9-paul@xen.org>
In-Reply-To: <20231122121822.1042-1-paul@xen.org>
References: <20231122121822.1042-1-paul@xen.org>
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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>

v9:
 - Pass both GPA and HVA into __kvm_gpc_refresh() rather than overloading
   the address paraneter and using a bool flag to indicated what it is.

v8:
 - Re-worked to avoid messing with struct gfn_to_pfn_cache.
---
 include/linux/kvm_host.h | 19 ++++++++++++++++++-
 virt/kvm/pfncache.c      | 35 +++++++++++++++++++++++++++--------
 2 files changed, 45 insertions(+), 9 deletions(-)

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 97eec8ee3449..c2a2d1e145b6 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -209,11 +209,13 @@ 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, gpa_t gpa, unsigned long uhva,
 			     unsigned long len)
 {
 	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
-	unsigned long page_offset = offset_in_page(gpa);
+	unsigned long page_offset = (gpa != KVM_XEN_INVALID_GPA) ?
+		offset_in_page(gpa) :
+		offset_in_page(uhva);
 	bool unmap_old = false;
 	unsigned long old_uhva;
 	kvm_pfn_t old_pfn;
@@ -246,9 +248,15 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
 	old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 	old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);
 
-	/* Refresh the userspace HVA if necessary */
-	if (gpc->gpa != gpa || gpc->generation != slots->generation ||
-	    kvm_is_error_hva(gpc->uhva)) {
+	if (gpa == KVM_XEN_INVALID_GPA) {
+		gpc->gpa = KVM_XEN_INVALID_GPA;
+		gpc->uhva = PAGE_ALIGN_DOWN(uhva);
+
+		if (gpc->uhva != old_uhva)
+			hva_change = true;
+	} else if (gpc->gpa != gpa ||
+		   gpc->generation != slots->generation ||
+		   kvm_is_error_hva(gpc->uhva)) {
 		gfn_t gfn = gpa_to_gfn(gpa);
 
 		gpc->gpa = gpa;
@@ -319,7 +327,7 @@ 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);
+	return __kvm_gpc_refresh(gpc, gpc->gpa, gpc->uhva, len);
 }
 
 void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
@@ -332,7 +340,8 @@ 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, gpa_t gpa, unsigned long uhva,
+			      unsigned long len)
 {
 	struct kvm *kvm = gpc->kvm;
 
@@ -353,7 +362,17 @@ 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, gpa, uhva, len);
+}
+
+int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
+{
+	return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len);
+}
+
+int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
+{
+	return __kvm_gpc_activate(gpc, KVM_XEN_INVALID_GPA, uhva, len);
 }
 
 void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
-- 
2.39.2