linux-kernel - [PATCH] KVM: nVMX: allow tests to use bad virtual-APIC page address

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Date:   Mon, 15 Apr 2019 15:35:33 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH] KVM: nVMX: allow tests to use bad virtual-APIC page address

As mentioned in the comment, there are some special cases where we can simply
clear the TPR shadow bit from the CPU-based execution controls in the vmcs02.
Handle them so that we can remove some XFAILs from vmx.flat.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 25 ++++++++++++++++---------
 arch/x86/kvm/vmx/vmx.c    |  2 +-
 arch/x86/kvm/vmx/vmx.h    |  2 ++
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 7ec9bb1dd723..a22af5a85540 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2873,20 +2873,27 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 		/*
 		 * If translation failed, VM entry will fail because
 		 * prepare_vmcs02 set VIRTUAL_APIC_PAGE_ADDR to -1ull.
-		 * Failing the vm entry is _not_ what the processor
-		 * does but it's basically the only possibility we
-		 * have.  We could still enter the guest if CR8 load
-		 * exits are enabled, CR8 store exits are enabled, and
-		 * virtualize APIC access is disabled; in this case
-		 * the processor would never use the TPR shadow and we
-		 * could simply clear the bit from the execution
-		 * control.  But such a configuration is useless, so
-		 * let's keep the code simple.
 		 */
 		if (!is_error_page(page)) {
 			vmx->nested.virtual_apic_page = page;
 			hpa = page_to_phys(vmx->nested.virtual_apic_page);
 			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, hpa);
+		} else if (nested_cpu_has(vmcs12, CPU_BASED_CR8_LOAD_EXITING) &&
+		           nested_cpu_has(vmcs12, CPU_BASED_CR8_STORE_EXITING) &&
+			   !nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
+			/*
+			 * The processor will never use the TPR shadow, simply
+			 * clear the bit from the execution control.  Such a
+			 * configuration is useless, but it happens in tests.
+			 * For any other configuration, failing the vm entry is
+			 * _not_ what the processor does but it's basically the
+			 * only possibility we have.
+			 */
+			vmcs_clear_bits(CPU_BASED_VM_EXEC_CONTROL,
+					CPU_BASED_TPR_SHADOW);
+		} else {
+			printk("bad virtual-APIC page address\n");
+			dump_vmcs();
 		}
 	}
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f8054dc1de65..14cacfd7ffd0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5603,7 +5603,7 @@ static void vmx_dump_dtsel(char *name, uint32_t limit)
 	       vmcs_readl(limit + GUEST_GDTR_BASE - GUEST_GDTR_LIMIT));
 }
 
-static void dump_vmcs(void)
+void dump_vmcs(void)
 {
 	u32 vmentry_ctl = vmcs_read32(VM_ENTRY_CONTROLS);
 	u32 vmexit_ctl = vmcs_read32(VM_EXIT_CONTROLS);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index a1e00d0a2482..f879529906b4 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -517,4 +517,6 @@ static inline void decache_tsc_multiplier(struct vcpu_vmx *vmx)
 	vmcs_write64(TSC_MULTIPLIER, vmx->current_tsc_ratio);
 }
 
+void dump_vmcs(void);
+
 #endif /* __KVM_X86_VMX_H */
-- 
1.8.3.1