KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit

Bus lock debug exception introduces a new bit DR6_BUS_LOCK (bit 11 of
DR6) to indicate that bus lock #DB exception is generated. The set/clear
of DR6_BUS_LOCK is similar to the DR6_RTM. The processor clears
DR6_BUS_LOCK when the exception is generated. For all other #DB, the
processor sets this bit to 1. Software #DB handler should set this bit
before returning to the interrupted task.

In VMM, to avoid breaking the CPUs without bus lock #DB exception
support, activate the DR6_BUS_LOCK conditionally in DR6_FIXED_1 bits.
When intercepting the #DB exception caused by bus locks, bit 11 of the
exit qualification is set to identify it. The VMM should emulate the
exception by clearing the bit 11 of the guest DR6.

Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Message-Id: <20210202090433.13441-3-chenyi.qiang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f85480b1d215f1c10f56fa9f232fbcf3242e2042..8836b30962178ff3ddbce5b827659d16339cfd37 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -200,6 +200,7 @@ enum x86_intercept_stage;
 
 #define KVM_NR_DB_REGS 4
 
+#define DR6_BUS_LOCK   (1 << 11)
 #define DR6_BD         (1 << 13)
 #define DR6_BS         (1 << 14)
 #define DR6_BT         (1 << 15)
@@ -213,7 +214,7 @@ enum x86_intercept_stage;
  * DR6_ACTIVE_LOW is also used as the init/reset value for DR6.
  */
 #define DR6_ACTIVE_LOW 0xffff0ff0
-#define DR6_VOLATILE   0x0001e00f
+#define DR6_VOLATILE   0x0001e80f
 #define DR6_FIXED_1    (DR6_ACTIVE_LOW & ~DR6_VOLATILE)
 
 #define DR7_BP_EN_MASK 0x000000ff

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4efd2978ec089470763a557cc34804dd411c13a7..9b1a7040eae3124d6e2ee260c36f0f04e3bc6f0e 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1176,6 +1176,9 @@ static u64 kvm_dr6_fixed(struct kvm_vcpu *vcpu)
 
        if (!guest_cpuid_has(vcpu, X86_FEATURE_RTM))
                fixed |= DR6_RTM;
+
+       if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
+               fixed |= DR6_BUS_LOCK;
        return fixed;
 }