[RFC PATCH 1/2] kvm/x86: intercept guest changes to X86_CR4_LA57

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

When shadowpaping is enabled, guest should not be allowed
to toggle X86_CR4_LA57. And X86_CR4_LA57 is a rarely changed
bit, so we can just intercept all the attempts to toggle it
no matter shadowpaping is in used or not.

Fixes: fd8cb433734ee ("KVM: MMU: Expose the LA57 feature to VM.")
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
  No test to toggle X86_CR4_LA57 in guest since I can't access to
  any CPU supports it. Maybe it is not a real problem.

 arch/x86/kvm/kvm_cache_regs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index cfe83d4ae625..ca0781b41df9 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -7,7 +7,7 @@
 #define KVM_POSSIBLE_CR0_GUEST_BITS X86_CR0_TS
 #define KVM_POSSIBLE_CR4_GUEST_BITS				  \
 	(X86_CR4_PVI | X86_CR4_DE | X86_CR4_PCE | X86_CR4_OSFXSR  \
-	 | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_PGE | X86_CR4_TSD)
+	 | X86_CR4_OSXMMEXCPT | X86_CR4_PGE | X86_CR4_TSD)
 
 #define BUILD_KVM_GPR_ACCESSORS(lname, uname)				      \
 static __always_inline unsigned long kvm_##lname##_read(struct kvm_vcpu *vcpu)\
-- 
2.19.1.6.gb485710b