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SubjectRe: [PATCH 0/3] KVM: VMX: Allow to disable ioport intercept per-VM by userspace
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 <>

Thank you.

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