[PATCH 0/7] x86, KVM: Optimize SEV cache flushing

Sean Christopherson
2025-02-27T01:49:04Z

This is the combination of Kevin's WBNOINVD series[1] with Zheyun's targeted
flushing series[2]. This is very, very lightly tested (emphasis on "very").

Note, I dropped Reviewed-by tags for patches to which I made non-trivial
modifications.

[1] https://lore.kernel.org/all/20250201000259.3289143-1-kevinloughlin@google.com
[2] https://lore.kernel.org/all/20250128015345.7929-1-szy0127@sjtu.edu.cn

Relative to those series:

- Name the WBNOINVD opcode macro ASM_WBNOINVD to avoid a conflict with
KVM's CPUID stuff.
- Fix issues with SMP=n.
- Define all helpers in x86/lib.
- Don't return 0 from the helpers.
- Rename the CPU bitmap to avoid a naming collisions with KVM's existing
pCPU bitmap for WBINVD, and to not have WBINVD (versus WBNOINVD) in the
name.
- Fix builds where CPU bitmaps are off-stack.
- Massage comments.
- Mark a CPU as having done VMRUN in pre_sev_run(), but test to see if
the CPU already ran to avoid the locked RMW, i.e. to (hopefully) avoid
bouncing the cache line.

Kevin Loughlin (2):
x86, lib: Add WBNOINVD helper functions
KVM: SEV: Prefer WBNOINVD over WBINVD for cache maintenance efficiency

Sean Christopherson (2):
x86, lib: Drop the unused return value from wbinvd_on_all_cpus()
KVM: x86: Use wbinvd_on_cpu() instead of an open-coded equivalent

Zheyun Shen (3):
KVM: SVM: Remove wbinvd in sev_vm_destroy()
x86, lib: Add wbinvd and wbnoinvd helpers to target multiple CPUs
KVM: SVM: Flush cache only on CPUs running SEV guest

arch/x86/include/asm/smp.h | 23 ++++++--
arch/x86/include/asm/special_insns.h | 19 ++++++-
arch/x86/kvm/svm/sev.c | 79 +++++++++++++++++++---------
arch/x86/kvm/svm/svm.h | 1 +
arch/x86/kvm/x86.c | 11 +---
arch/x86/lib/cache-smp.c | 26 ++++++++-
6 files changed, 119 insertions(+), 40 deletions(-)

base-commit: fed48e2967f402f561d80075a20c5c9e16866e53