> From: Yongji Xie [mailto:xyjxie@xxxxxxxxxxxxxxxxxx] > Sent: Tuesday, May 03, 2016 2:08 PM > > On 2016/5/3 13:34, Tian, Kevin wrote: > > >> From: Yongji Xie > >> Sent: Wednesday, April 27, 2016 8:43 PM > >> > >> This patch enables mmapping MSI-X tables if hardware supports > >> interrupt remapping which can ensure that a given pci device > >> can only shoot the MSIs assigned for it. > >> > >> With MSI-X table mmapped, we also need to expose the > >> read/write interface which will be used to access MSI-X table. > >> > >> Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx> > > A curious question here. Does "allow to mmap MSI-X" essentially > > mean that KVM guest can directly read/write physical MSI-X > > structure then? > > > > Thanks > > Kevin > > > > Here we just allow to mmap MSI-X table in kernel. It doesn't > mean all KVM guest can directly read/write physical MSI-X > structure. This should be decided by QEMU. For PPC64 > platform, we would allow to passthrough the MSI-X table > because we know guest kernel would not write physical > MSI-X structure when enabling MSI. > A bit confused here. If guest kernel doesn't need to write physical MSI-X structure, what's the point of passing through the table then? I think the key whether MSI-X table can be passed through is related to where hypervisor control is deployed. At least for x86: - When irq remapping is not enabled, host/hypervisor needs to control physical interrupt message including vector/dest/etc. directly in MSI-X structure, so we cannot allow a guest to access it; - when irq remapping is enabled, host/hypervisor can control interrupt routing in irq remapping table. However MSI-X also needs to be configured as remappable format. In this manner we also cannot allow direct access from guest. The only sane case to pass through MSI-X structure, is a mechanism similar to irq remapping but w/o need to change original MSI-X format so direct access from guest side is safe. Is it the case in PPC64? Thanks Kevin ��.n��������+%������w��{.n�����{���"�)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
