AMD CPUs currently execute WBINVD in the host when unregistering SEV guest memory or when deactivating SEV guests. Such cache maintenance is performed to prevent data corruption, wherein the encrypted (C=1) version of a dirty cache line might otherwise only be written back after the memory is written in a different context (ex: C=0), yielding corruption. However, WBINVD is performance-costly, especially because it invalidates processor caches. Strictly-speaking, unless the SEV ASID is being recycled (meaning all existing cache lines with the recycled ASID must be flushed), the cache invalidation triggered by WBINVD is unnecessary; only the writeback is needed to prevent data corruption in remaining scenarios. To improve performance in these scenarios, use WBNOINVD when available instead of WBINVD. WBNOINVD still writes back all dirty lines (preventing host data corruption by SEV guests) but does *not* invalidate processor caches. First, provide helper functions to use WBINVD similar to how WBINVD is invoked. Second, check for WBNOINVD support and execute WBNOINVD if possible in lieu of WBINVD to avoid cache invalidations Kevin Loughlin (2): x86, lib, xenpv: Add WBNOINVD helper functions KVM: SEV: Prefer WBNOINVD over WBINVD for cache maintenance efficiency arch/x86/include/asm/paravirt.h | 7 ++++++ arch/x86/include/asm/paravirt_types.h | 1 + arch/x86/include/asm/smp.h | 7 ++++++ arch/x86/include/asm/special_insns.h | 12 ++++++++- arch/x86/kernel/paravirt.c | 6 +++++ arch/x86/kvm/svm/sev.c | 35 +++++++++++++++++---------- arch/x86/lib/cache-smp.c | 12 +++++++++ arch/x86/xen/enlighten_pv.c | 1 + 8 files changed, 67 insertions(+), 14 deletions(-) -- 2.47.0.338.g60cca15819-goog
