linux-kernel - [PATCH v4 0/2] KVM: nested VPID emulation

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Date:	Wed, 16 Sep 2015 15:19:08 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	Jan Kiszka <jan.kiszka@...mens.com>, Bandan Das <bsd@...hat.com>,
	Wincy Van <fanwenyi0529@...il.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH v4 0/2] KVM: nested VPID emulation

v3 -> v4:
 * return 0 if vpid == VMX_NR_VPIDs
 * skip vpid != 0 check

v2 -> v3:
 * enhance allocate/free_vpid as Jan's suggestion
 * add more comments to 2/2

v1 -> v2:
 * enhance allocate/free_vpid to handle shadow vpid
 * drop empty space
 * allocate shadow vpid during initialization
 * For each nested vmentry, if vpid12 is changed, reuse shadow vpid w/ an 
   invvpid.

VPID is used to tag address space and avoid a TLB flush. Currently L0 use 
the same VPID to run L1 and all its guests. KVM flushes VPID when switching 
between L1 and L2. 

This patch advertises VPID to the L1 hypervisor, then address space of L1 and 
L2 can be separately treated and avoid TLB flush when swithing between L1 and 
L2.

Performance: 

run lmbench on L2 w/ 3.5 kernel.

Context switching - times in microseconds - smaller is better
-------------------------------------------------------------------------
Host                 OS  2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
                         ctxsw  ctxsw  ctxsw ctxsw  ctxsw   ctxsw   ctxsw
--------- ------------- ------ ------ ------ ------ ------ ------- -------
kernel    Linux 3.5.0-1 1.2200 1.3700 1.4500 4.7800 2.3300 5.60000 2.88000  nested VPID 
kernel    Linux 3.5.0-1 1.2600 1.4300 1.5600   12.7   12.9 3.49000 7.46000  vanilla

Wanpeng Li (2):
  KVM: nVMX: enhance allocate/free_vpid to handle shadow vpid
  KVM: nVMX: nested VPID emulation

 arch/x86/kvm/vmx.c | 60 ++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 42 insertions(+), 18 deletions(-)

-- 
1.9.1

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