A recent commit reworked __kvm_handle_fault_on_reboot() to play nice with
objtool. An unfortunate side effect is that JMP is now inserted after
most VMX instructions so that the reboot macro can use an actual CALL to
kvm_spurious_fault() instead of a funky PUSH+JMP facsimile in .fixup.
Rework the low level VMX instruction helpers to handle unexpected faults
manually instead of relying on the "fault on reboot" macro. By using
asm-goto, most helpers can branch directly to an in-function call to
kvm_spurious_fault(), which can then be optimized by compilers to reside
out-of-line at the end of the function instead of inline as done by
"fault on reboot".
The net impact relative to the current code base is more or less a nop
when building with a compiler that supports __GCC_ASM_FLAG_OUTPUTS__.
A bunch of code that was previously in .fixup gets moved into the slow
paths of functions, but the fast paths are more basically unchanged.
Without __GCC_ASM_FLAG_OUTPUTS__, manually coding the Jcc is a net
positive as CC_SET() without compiler support almost always generates a
SETcc+CMP+Jcc sequence, which is now replaced with a single Jcc.
A small bonus is that the Jcc instrs are hinted to predict that the VMX
instr will be successful.
v2:
- Rebased to x86/master, commit eceffd88ca20 ("Merge branch 'x86/urgent'")
- Reworded changelogs to reference the commit instead lkml link for
the recent changes to __kvm_handle_fault_on_reboot().
- Added Paolo's acks for patch 1-4
- Added patch 5 to do more cleanup, which was made possible by rebasing
on top of the __kvm_handle_fault_on_reboot() changes.
Sean Christopherson (5):
objtool: KVM: x86: Check kvm_rebooting in kvm_spurious_fault()
KVM: VMX: Optimize VMX instruction error and fault handling
KVM: VMX: Add error handling to VMREAD helper
KVM: x86: Drop ____kvm_handle_fault_on_reboot()
KVM: x86: Don't check kvm_rebooting in __kvm_handle_fault_on_reboot()
arch/x86/include/asm/kvm_host.h | 16 ++----
arch/x86/kvm/vmx/ops.h | 93 ++++++++++++++++++++-------------
arch/x86/kvm/vmx/vmx.c | 42 +++++++++++++++
arch/x86/kvm/x86.c | 3 +-
tools/objtool/check.c | 1 -
5 files changed, 104 insertions(+), 51 deletions(-)
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2.22.0
