[Xen-changelog] [xen master] x86/hvm: Adjust hvm_nx_enabled() to match how Xen behaves

[patchbot@xxxxxxx]

commit 7bdb974a82c1631bfc7451b9dd9756858617aef4
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jul 5 10:40:21 2016 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Mar 2 18:44:09 2017 +0000

    x86/hvm: Adjust hvm_nx_enabled() to match how Xen behaves
    
    On Intel hardware, EFER is not fully switched between host and guest 
contexts.
    In practice, this means that Xen's EFER.NX setting leaks into guest context,
    and influences the behaviour of the hardware pagewalker.
    
    When servicing a pagefault, Xen's model of guests behaviour should match
    hardware's behaviour, to allow correct interpretation of the pagefault error
    code, and to avoid creating observable difference in behaviour from the 
guests
    point of view.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/include/asm-x86/hvm/hvm.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 87b203a..eccc25e 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -292,8 +292,10 @@ int hvm_girq_dest_2_vcpu_id(struct domain *d, uint8_t 
dest, uint8_t dest_mode);
     (hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_SMEP))
 #define hvm_smap_enabled(v) \
     (hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_SMAP))
+/* HVM guests on Intel hardware leak Xen's NX settings into guest context. */
 #define hvm_nx_enabled(v) \
-    (!!((v)->arch.hvm_vcpu.guest_efer & EFER_NX))
+    ((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL && cpu_has_nx) ||    \
+     ((v)->arch.hvm_vcpu.guest_efer & EFER_NX))
 #define hvm_pku_enabled(v) \
     (hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_PKE))
 
--
generated by git-patchbot for /home/xen/git/xen.git#master

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