linux-kernel - [PATCH v4 0/3] KVM: SVM: Refactor vcpu_load/put to use vmload/vmsave for host state

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Date:   Tue,  2 Feb 2021 13:01:23 -0600
From:   Michael Roth <michael.roth@....com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 0/3] KVM: SVM: Refactor vcpu_load/put to use vmload/vmsave for host state

Hi Sean, Paolo,

Following up from previous v3 discussion:

  https://lore.kernel.org/kvm/X%2FSfw15OWarseivB@google.com/

I got bit in internal testing by a bug in v3 of this series that Sean had
already pointed out in v3 comments, so I thought it might be good to go
ahead and send a v4 with those fixes included. I also saw that Sean's vmsave
helpers are now in kvm/queue, so I've rebased these on top of those, and
made use of the new vmsave/vmload helpers:

  https://lore.kernel.org/kvm/8880fedc-14aa-1f14-b87b-118ebe0932a2@redhat.com/

Thanks!

-Mike

= Overview =

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).

v4:
 - rebased on kvm/queue
 - use sme_page_pa() when accessing save area (Sean)
 - make sure vmload during host reboot is handled (Sean)
 - introduce vmload() helper like we have with vmsave(), use that instead
   of moving the introduce to ASM (Sean)

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     | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------------------------
 arch/x86/kvm/svm/svm.h     |  29 +++++------------------------
 arch/x86/kvm/svm/svm_ops.h |   5 +++++
 4 files changed, 67 insertions(+), 104 deletions(-)