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SubjectRe: [PATCH 0/3] KVM: VMX: Allow to disable ioport intercept per-VM by userspace
2018-05-11 23:40 GMT+08:00 Konrad Rzeszutek Wilk <>:
> On Mon, Apr 16, 2018 at 10:45:59PM -0700, Wanpeng Li wrote:
>> Tim Shearer reported that "There is a guest which is running a packet
>> forwarding app based on the DPDK ( The packet receive routine
>> writes to 0xc070 using glibc's "outw_p" function which does an additional
>> write to I/O port 0x80. It does this write for every packet that's
>> received, causing a flood of KVM userspace context switches". He uses
>> mpstat to observe a CPU performing L2 packet forwarding on a pinned
>> guest vCPU, the guest time is 95 percent when allowing I/O port 0x80
>> bypass, however, it is 65.78 percent when I/O port 0x80 bypss is
>> disabled.
>> This patchset introduces per-VM I/O permission bitmaps, the userspace
>> can disable the ioport intercept when they are more concern the
>> performance than the security.
> Could you kindly also add:
> Suggested-by: Konrad Rzeszutek Wilk <>

Yeah, both you and Liran give the original idea. :) Tim and Liran, any
review for the patchset?

Wanpeng Li

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