[0/3] KVM: SVM: Refactor vcpu_load/put to use vmload/vmsave for host state

Message

Michael Roth Jan. 5, 2021, 2:37 p.m. UTC

This series re-works the SVM KVM implementation to use vmload/vmsave to
handle saving/restoring additional host MSRs rather than explicit MSR
read/writes, resulting in a significant performance improvement for some
specific workloads and simplifying some of the save/load code (PATCH 1).

With those changes some commonalities emerge between SEV-ES and normal
vcpu_load/vcpu_put paths, which we then take advantage of to share more code,
as well as refactor them in a way that more closely aligns with the VMX
implementation (PATCH 2 and 3).

v3:
 - rebased on kvm-next
 - remove uneeded braces from host MSR save/load loops (Sean)
 - use page_to_phys() in place of page_to_pfn() and shifting (Sean)
 - use stack instead of struct field to cache host save area outside of
   per-cpu storage, and pass as an argument to __svm_vcpu_run() to
   handle the VMLOAD in ASM code rather than inlining ASM (Sean/Andy)
 - remove now-uneeded index/sev_es_restored fields from
   host_save_user_msrs list
 - move host-saving/guest-loading of registers to prepare_guest_switch(),
   and host-loading of registers to prepare_host_switch, for both normal
   and sev-es paths (Sean)

v2:
 - rebase on latest kvm/next
 - move VMLOAD to just after vmexit so we can use it to handle all FS/GS
   host state restoration and rather than relying on loadsegment() and
   explicit write to MSR_GS_BASE (Andy)
 - drop 'host' field from struct vcpu_svm since it is no longer needed
   for storing FS/GS/LDT state (Andy)

 arch/x86/kvm/svm/sev.c     |  30 +-----------------------------
 arch/x86/kvm/svm/svm.c     | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------------------------------------------------------
 arch/x86/kvm/svm/svm.h     |  31 ++++++-------------------------
 arch/x86/kvm/svm/vmenter.S |  10 ++++++++++
 4 files changed, 75 insertions(+), 108 deletions(-)