From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: kvm@vger.kernel.org
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Jim Mattson" <jmattson@google.com>,
"Liran Alon" <liran.alon@oracle.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH RFC 0/7] x86/kvm/nVMX: optimize MMU switch between L1 and L2
Date: Fri, 20 Jul 2018 15:26:19 +0200 [thread overview]
Message-ID: <20180720132626.5975-1-vkuznets@redhat.com> (raw)
Currently, when we switch from L1 to L2 we do the following:
- Re-initialize L1 MMU as shadow EPT MMU (nested_ept_init_mmu_context())
- Re-initialize 'nested' MMU (nested_vmx_load_cr3() -> init_kvm_nested_mmu())
- Reload MMU root upon guest entry.
When we switch back we do:
- Re-initialize L1 MMU (nested_vmx_load_cr3() -> init_kvm_tdp_mmu())
- Reload MMU root upon guest entry.
This seems to be sub-optimal. Initializing MMU is expensive (thanks to
update_permission_bitmask(), update_pkru_bitmask(),..) and reloading MMU
root doesn't come for free.
Try to approach the issue by splitting L1-normal and L1-nested MMUs and
checking if MMU reset is really needed. This spares us about 1000 cpu
cycles on nested vmexit.
RFC part:
- Does this look like a plausible solution?
- SVM nested can probably be optimized in the same way.
- Doesn mmu_update_needed() cover everything?
Vitaly Kuznetsov (7):
x86/kvm/mmu: make vcpu->mmu a pointer to the current MMU
x86/kvm/mmu.c: set get_pdptr hook in kvm_init_shadow_ept_mmu()
x86/kvm/mmu.c: add kvm_mmu parameter to kvm_mmu_free_roots()
x86/kvm/mmu: introduce guest_mmu
x86/kvm/mmu: get rid of redundant kvm_mmu_setup()
x86/kvm/nVMX: introduce scache for kvm_init_shadow_ept_mmu
x86/kvm/nVMX: optimize MMU switch from nested_vmx_load_cr3()
arch/x86/include/asm/kvm_host.h | 36 ++++-
arch/x86/kvm/cpuid.c | 2 +-
arch/x86/kvm/mmu.c | 282 ++++++++++++++++++++++++++--------------
arch/x86/kvm/mmu.h | 2 +-
arch/x86/kvm/mmu_audit.c | 12 +-
arch/x86/kvm/paging_tmpl.h | 17 +--
arch/x86/kvm/svm.c | 20 +--
arch/x86/kvm/vmx.c | 52 +++++---
arch/x86/kvm/x86.c | 34 ++---
9 files changed, 292 insertions(+), 165 deletions(-)
--
2.14.4
next reply other threads:[~2018-07-20 13:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-20 13:26 Vitaly Kuznetsov [this message]
2018-07-20 13:26 ` [PATCH RFC 1/7] x86/kvm/mmu: make vcpu->mmu a pointer to the current MMU Vitaly Kuznetsov
2018-07-20 13:26 ` [PATCH RFC 2/7] x86/kvm/mmu.c: set get_pdptr hook in kvm_init_shadow_ept_mmu() Vitaly Kuznetsov
2018-07-20 13:26 ` [PATCH RFC 3/7] x86/kvm/mmu.c: add kvm_mmu parameter to kvm_mmu_free_roots() Vitaly Kuznetsov
2018-07-20 13:26 ` [PATCH RFC 4/7] x86/kvm/mmu: introduce guest_mmu Vitaly Kuznetsov
2018-07-20 13:26 ` [PATCH RFC 5/7] x86/kvm/mmu: get rid of redundant kvm_mmu_setup() Vitaly Kuznetsov
2018-07-20 13:26 ` [PATCH RFC 6/7] x86/kvm/nVMX: introduce scache for kvm_init_shadow_ept_mmu Vitaly Kuznetsov
2018-07-20 13:26 ` [PATCH RFC 7/7] x86/kvm/nVMX: optimize MMU switch from nested_vmx_load_cr3() Vitaly Kuznetsov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180720132626.5975-1-vkuznets@redhat.com \
--to=vkuznets@redhat.com \
--cc=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=liran.alon@oracle.com \
--cc=pbonzini@redhat.com \
--cc=rkrcmar@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).