linux-kernel - [RFC PATCH 1/2] kvm/x86: intercept guest changes to X86_CR4

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Message-Id: <20200928083047.3349-1-jiangshanlai@gmail.com>
Date:   Mon, 28 Sep 2020 16:30:46 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: [RFC PATCH 1/2] kvm/x86: intercept guest changes to X86_CR4_LA57

From: Lai Jiangshan <laijs@...ux.alibaba.com>

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@...el.com>
Cc: Yu Zhang <yu.c.zhang@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
  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