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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 1/2] KVM: xen: separate initialization of shared_info cache and content
Date:   Fri,  1 Dec 2023 10:45:35 +0000
Message-Id: <20231201104536.947-2-paul@xen.org>
In-Reply-To: <20231201104536.947-1-paul@xen.org>
References: <20231201104536.947-1-paul@xen.org>
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From: Paul Durrant <pdurrant@amazon.com>

The shared_info cache should only need to be set up once by the VMM, but
the content of the shared_info page may need changed if the mode of guest
changes from 32-bit to 64-bit or vice versa. This re-initialization of
the content will be handles in a subsequent patch.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
 arch/x86/kvm/xen.c | 70 ++++++++++++++++++++++++++--------------------
 1 file changed, 40 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index cfd5051e0800..7bead3f65e55 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -34,7 +34,7 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r);
 
 DEFINE_STATIC_KEY_DEFERRED_FALSE(kvm_xen_enabled, HZ);
 
-static int kvm_xen_shared_info_init(struct kvm *kvm, u64 addr, bool addr_is_gfn)
+static int kvm_xen_shared_info_init(struct kvm *kvm)
 {
 	struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
 	struct pvclock_wall_clock *wc;
@@ -44,34 +44,22 @@ static int kvm_xen_shared_info_init(struct kvm *kvm, u64 addr, bool addr_is_gfn)
 	int ret = 0;
 	int idx = srcu_read_lock(&kvm->srcu);
 
-	if ((addr_is_gfn && addr == KVM_XEN_INVALID_GFN) ||
-	    (!addr_is_gfn && addr == 0)) {
-		kvm_gpc_deactivate(gpc);
-		goto out;
-	}
+	read_lock_irq(&gpc->lock);
+	while (!kvm_gpc_check(gpc, PAGE_SIZE)) {
+		read_unlock_irq(&gpc->lock);
 
-	do {
-		if (addr_is_gfn)
-			ret = kvm_gpc_activate(gpc, gfn_to_gpa(addr), PAGE_SIZE);
-		else
-			ret = kvm_gpc_activate_hva(gpc, addr, PAGE_SIZE);
+		ret = kvm_gpc_refresh(gpc, PAGE_SIZE);
 		if (ret)
 			goto out;
 
-		/*
-		 * This code mirrors kvm_write_wall_clock() except that it writes
-		 * directly through the pfn cache and doesn't mark the page dirty.
-		 */
-		wall_nsec = kvm_get_wall_clock_epoch(kvm);
-
-		/* It could be invalid again already, so we need to check */
 		read_lock_irq(&gpc->lock);
+	}
 
-		if (gpc->valid)
-			break;
-
-		read_unlock_irq(&gpc->lock);
-	} while (1);
+	/*
+	 * This code mirrors kvm_write_wall_clock() except that it writes
+	 * directly through the pfn cache and doesn't mark the page dirty.
+	 */
+	wall_nsec = ktime_get_real_ns() - get_kvmclock_ns(kvm);
 
 	/* Paranoia checks on the 32-bit struct layout */
 	BUILD_BUG_ON(offsetof(struct compat_shared_info, wc) != 0x900);
@@ -642,17 +630,39 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		break;
 
 	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
-		mutex_lock(&kvm->arch.xen.xen_lock);
-		r = kvm_xen_shared_info_init(kvm, data->u.shared_info.gfn, true);
-		mutex_unlock(&kvm->arch.xen.xen_lock);
-		break;
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA: {
+		int idx;
 
-	case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA:
 		mutex_lock(&kvm->arch.xen.xen_lock);
-		r = kvm_xen_shared_info_init(kvm, data->u.shared_info.hva, false);
+
+		idx = srcu_read_lock(&kvm->srcu);
+		if (data->type == KVM_XEN_ATTR_TYPE_SHARED_INFO) {
+			if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) {
+				kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
+				r = 0;
+			} else {
+				r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache,
+						     gfn_to_gpa(data->u.shared_info.gfn),
+						     PAGE_SIZE);
+			}
+		} else {
+			if (data->u.shared_info.hva == 0) {
+				kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
+				r = 0;
+			} else {
+				r = kvm_gpc_activate_hva(&kvm->arch.xen.shinfo_cache,
+							 data->u.shared_info.hva,
+							 PAGE_SIZE);
+			}
+		}
+		srcu_read_unlock(&kvm->srcu, idx);
+
+		if (!r && kvm->arch.xen.shinfo_cache.active)
+			r = kvm_xen_shared_info_init(kvm);
+
 		mutex_unlock(&kvm->arch.xen.xen_lock);
 		break;
-
+	}
 	case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
 		if (data->u.vector && data->u.vector < 0x10)
 			r = -EINVAL;
-- 
2.39.2