[PATCH v2 0/4] x86/cpu: Add Bus Lock Detect support for AMD

[Ravi Bangoria]

Upcoming AMD uarch will support Bus Lock Detect (called Bus Lock Trap
in AMD docs). Add support for the same in Linux. Bus Lock Detect is
enumerated with cpuid CPUID Fn0000_0007_ECX_x0 bit [24 / BUSLOCKTRAP].
It can be enabled through MSR_IA32_DEBUGCTLMSR. When enabled, hardware
clears DR6[11] and raises a #DB exception on occurrence of Bus Lock if
CPL > 0. More detail about the feature can be found in AMD APM[1].

Patches are prepared on tip/master (a6fffa92da54).

[1]: AMD64 Architecture Programmer's Manual Pub. 40332, Rev. 4.07 - June
     2023, Vol 2, 13.1.3.6 Bus Lock Trap
     https://bugzilla.kernel.org/attachment.cgi?id=304653

v1: https://lore.kernel.org/r/20240429060643.211-1-ravi.bangoria@xxxxxxx
v1->v2:
- Call bus_lock_init() from common.c. Although common.c is shared across
  all X86_VENDOR_*, bus_lock_init() internally checks for
  X86_FEATURE_BUS_LOCK_DETECT, hence it's safe to call it from common.c.
- s/split-bus-lock.c/bus_lock.c/ for a new filename.
- Add a KVM patch to disable Bus Lock Trap unconditionally when SVM
  support is missing.

Note:
A Qemu fix is also require to handle corner case where a hardware
instruction or data breakpoint is created by Qemu remote debugger (gdb)
on the same instruction which also causes a Bus Lock. I'll post a Qemu
patch separately.

Ravi Bangoria (4):
  x86/split_lock: Move Split and Bus lock code to a dedicated file
  x86/bus_lock: Add support for AMD
  KVM: SVM: Don't advertise Bus Lock Detect to guest if SVM support is
    missing
  KVM: SVM: Add Bus Lock Detect support

 arch/x86/include/asm/cpu.h     |   4 +
 arch/x86/kernel/cpu/Makefile   |   1 +
 arch/x86/kernel/cpu/bus_lock.c | 406 ++++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/common.c   |   2 +
 arch/x86/kernel/cpu/intel.c    | 407 ---------------------------------
 arch/x86/kvm/svm/nested.c      |   3 +-
 arch/x86/kvm/svm/svm.c         |  16 +-
 7 files changed, 430 insertions(+), 409 deletions(-)
 create mode 100644 arch/x86/kernel/cpu/bus_lock.c

-- 
2.34.1