On Wed, 4 Jul 2018, Paolo Bonzini wrote: > On 04/07/2018 15:06, Jingqi Liu wrote: > > A new control bit(bit 29) in the TEST_CTRL MSR will be introduced > > to enable detection of split locks. > > > > When bit 29 of the TEST_CTRL(33H) MSR is set, the processor > > causes an #AC exception to be issued instead of suppressing LOCK on > > bus(during split lock access). A previous control bit (bit 31) > > in this MSR causes the processor to disable LOCK# assertion for > > split locked accesses when set. When bits 29 and 31 are both set, > > bit 29 takes precedence. > > > > The release document ref below link: > > https://software.intel.com/sites/default/files/managed/c5/15/\ > > architecture-instruction-set-extensions-programming-reference.pdf > > This patch has a dependency on https://lkml.org/lkml/2018/5/27/78. That dependency is useless, because that series is going nowhere. > > Signed-off-by: Jingqi Liu <jingqi.liu@xxxxxxxxx> > > --- > > arch/x86/include/asm/kvm_host.h | 1 + > > arch/x86/kvm/vmx.c | 77 +++++++++++++++++++++++++++++++++++++++++ > > arch/x86/kvm/x86.c | 10 ++++++ > > arch/x86/kvm/x86.h | 5 +++ > > include/uapi/linux/kvm.h | 1 + > > 5 files changed, 94 insertions(+) > > Checking for split lock is done with the MSR_TEST_CTL too, so you should > not use a capability to expose the availability to KVM userspace. > Instead you should expose the contents of MSR_TEST_CTL on the host, in a > similar way to https://marc.info/?l=kvm&m=152998661713547&w=2. > > Please coordinate with Robert Hu on the QEMU patches too, because he's > working on the infrastructure to use KVM_GET_MSR_FEATURE_INDEX_LIST in QEMU. Can we please sort out the whole AC mess on the host first including the detection stuff? There is no rush for this to be in KVM/QEMU now because all what exists for this new split lock thing is 'silicon' running on an emulator. And w/o support in the kernel proper this is completely useless. So this needs the following things: 1) Proper enumeration via CPUID or MISC_FEATURES. The current detection hack is just broken. 2) A proper host side implementation, which then automatically makes the stuff usable in a guest once it is exposed. 3) A proper way how to expose MSR_TEST_CTL to the guest, but surely not with extra split_lock_ctrl voodoo. It's an MSR nothing else. KVM/QEMU have standartized ways to deal with MSRs and the required selective bitwise access control. Thanks, tglx
