From: Nikunj A Dadhania nikunj@amd.com
Virtual machines can exploit bus locks to degrade the performance of the system. Bus locks can be caused by Non-WB(Write back) and misaligned locked RMW (Read-modify-Write) instructions and require systemwide synchronization among all processors which can result into significant performance penalties.
To address this issue, the Bus Lock Threshold feature is introduced to provide ability to hypervisor to restrict guests' capability of initiating mulitple buslocks, thereby preventing system slowdowns.
Support for the buslock threshold is indicated via CPUID function 0x8000000A_EDX[29].
On the processors that support the Bus Lock Threshold feature, the VMCB provides a Bus Lock Threshold enable bit and an unsigned 16-bit Bus Lock threshold count.
VMCB intercept bit VMCB Offset Bits Function 14h 5 Intercept bus lock operations
Bus lock threshold count VMCB Offset Bits Function 120h 15:0 Bus lock counter
When a VMRUN instruction is executed, the bus lock threshold count is loaded into an internal count register. Before the processor executes a bus lock in the guest, it checks the value of this register:
- If the value is greater than '0', the processor successfully executes the bus lock and decrements the count.
- If the value is '0', the bus lock is not executed, and a #VMEXIT to the VMM is taken.
The bus lock threshold #VMEXIT is reported to the VMM with the VMEXIT code A5h, SVM_EXIT_BUS_LOCK.
Signed-off-by: Nikunj A Dadhania nikunj@amd.com Co-developed-by: Manali Shukla manali.shukla@amd.com Signed-off-by: Manali Shukla manali.shukla@amd.com --- arch/x86/include/asm/svm.h | 7 +++++-- arch/x86/include/uapi/asm/svm.h | 2 ++ 2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h index b382fd251e5b..ad954a1a6656 100644 --- a/arch/x86/include/asm/svm.h +++ b/arch/x86/include/asm/svm.h @@ -116,6 +116,7 @@ enum { INTERCEPT_INVPCID, INTERCEPT_MCOMMIT, INTERCEPT_TLBSYNC, + INTERCEPT_BUSLOCK, INTERCEPT_IDLE_HLT = 166, };
@@ -159,10 +160,12 @@ struct __attribute__ ((__packed__)) vmcb_control_area { u64 avic_physical_id; /* Offset 0xf8 */ u8 reserved_7[8]; u64 vmsa_pa; /* Used for an SEV-ES guest */ - u8 reserved_8[40]; + u8 reserved_8[16]; + u16 bus_lock_counter; /* Offset 0x120 */ + u8 reserved_9[22]; u64 allowed_sev_features; /* Offset 0x138 */ u64 guest_sev_features; /* Offset 0x140 */ - u8 reserved_9[664]; + u8 reserved_10[664]; /* * Offset 0x3e0, 32 bytes reserved * for use by hypervisor/software. diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h index ec1321248dac..9c640a521a67 100644 --- a/arch/x86/include/uapi/asm/svm.h +++ b/arch/x86/include/uapi/asm/svm.h @@ -95,6 +95,7 @@ #define SVM_EXIT_CR14_WRITE_TRAP 0x09e #define SVM_EXIT_CR15_WRITE_TRAP 0x09f #define SVM_EXIT_INVPCID 0x0a2 +#define SVM_EXIT_BUS_LOCK 0x0a5 #define SVM_EXIT_IDLE_HLT 0x0a6 #define SVM_EXIT_NPF 0x400 #define SVM_EXIT_AVIC_INCOMPLETE_IPI 0x401 @@ -225,6 +226,7 @@ { SVM_EXIT_CR4_WRITE_TRAP, "write_cr4_trap" }, \ { SVM_EXIT_CR8_WRITE_TRAP, "write_cr8_trap" }, \ { SVM_EXIT_INVPCID, "invpcid" }, \ + { SVM_EXIT_BUS_LOCK, "buslock" }, \ { SVM_EXIT_IDLE_HLT, "idle-halt" }, \ { SVM_EXIT_NPF, "npf" }, \ { SVM_EXIT_AVIC_INCOMPLETE_IPI, "avic_incomplete_ipi" }, \