From: Sean Christopherson <seanjc@google.com>
Date: Thu, 10 Oct 2024 18:23:38 +0000 (-0700)
Subject: KVM: x86: Don't fault-in APIC access page during initial allocation
X-Git-Tag: v6.13-rc1~97^2~17^2~49
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=fcd366b95e6e356ae5069753938988b6c6286fa8;p=thirdparty%2Fkernel%2Flinux.git

KVM: x86: Don't fault-in APIC access page during initial allocation

Drop the gfn_to_page() lookup when installing KVM's internal memslot for
the APIC access page, as KVM doesn't need to immediately fault-in the page
now that the page isn't pinned.  In the extremely unlikely event the
kernel can't allocate a 4KiB page, KVM can just as easily return -EFAULT
on the future page fault.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-37-seanjc@google.com>
---

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 20526e4d6c625..65412640cfc77 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2647,7 +2647,6 @@ void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
 
 int kvm_alloc_apic_access_page(struct kvm *kvm)
 {
-	struct page *page;
 	void __user *hva;
 	int ret = 0;
 
@@ -2663,17 +2662,6 @@ int kvm_alloc_apic_access_page(struct kvm *kvm)
 		goto out;
 	}
 
-	page = gfn_to_page(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
-	if (!page) {
-		ret = -EFAULT;
-		goto out;
-	}
-
-	/*
-	 * Do not pin the page in memory, so that memory hot-unplug
-	 * is able to migrate it.
-	 */
-	put_page(page);
 	kvm->arch.apic_access_memslot_enabled = true;
 out:
 	mutex_unlock(&kvm->slots_lock);