[PATCH v13 34/85] KVM: Get writable mapping for __kvm_vcpu_map() only when necessary

[Sean Christopherson]

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.ben...@linaro.org>
Signed-off-by: Sean Christopherson <sea...@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 080740f65061..b845e9252633 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3122,7 +3122,7 @@ 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,
        };
-- 
2.47.0.rc1.288.g06298d1525-goog