From 2e5fdf60a9a69971b5e642d32e09bd6b0223f47c Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Thu, 10 Oct 2024 11:23:36 -0700
Subject: [PATCH] KVM: Get writable mapping for __kvm_vcpu_map() only when
necessary
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When creating a memory map for read, don't request a writable pfn from the
primary MMU. While creating read-only mappings can be theoretically slower,
as they don't play nice with fast GUP due to the need to break CoW before
mapping the underlying PFN, practically speaking, creating a mapping isn't
a super hot path, and getting a writable mapping for reading is weird and
confusing.
Tested-by: Alex Bennée <alex.bennee@linaro.org>
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: <20241010182427.1434605-35-seanjc@google.com>
---
virt/kvm/kvm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index baa741c2b81c4..49ac13872e091 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3116,7 +3116,7 @@ int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map,
struct kvm_follow_pfn kfp = {
.slot = gfn_to_memslot(vcpu->kvm, gfn),
.gfn = gfn,
- .flags = FOLL_WRITE,
+ .flags = writable ? FOLL_WRITE : 0,
.refcounted_page = &map->pinned_page,
.pin = true,
};
--
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