On Fri, Sep 15, 2017 at 5:26 AM, Auger Eric <eric.auger@xxxxxxxxxx> wrote: > Hi, > > On 14/09/2017 19:06, Marc Zyngier wrote: >> On Thu, Sep 14 2017 at 10:57:28 am BST, Eric Auger <eric.auger@xxxxxxxxxx> wrote: >>> At the moment, the in-kernel emulated ITS is not properly reset. >>> On guest restart/reset some registers keep their old values and >>> internal structures like device, ITE, collection lists are not emptied. >>> >>> This may lead to various bugs. Among them, we can have incorrect state >>> backup or failure when saving the ITS state at early guest boot stage. >>> >>> This patch introduces a new attribute, KVM_DEV_ARM_ITS_CTRL_RESET in >>> the KVM_DEV_ARM_VGIC_GRP_CTRL group. >>> >>> Upon this action, we can invalidate the various memory structures >>> pointed by GITS_BASERn and GITS_CBASER, free the ITS internal caches >>> and reset the relevant registers. >>> >>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx> >>> >>> --- >>> >>> An alternative would consist in having the userspace writing >>> individual registers with default values: GITS_BASERn, GITS_CBASER >>> and GITS_CTLR. On kernel side we would reset related lists when >>> detecting the valid bit is set to false. >> >> I'm not sure this is necessarily a "either/or" situation. It looks to me >> that we're not completely doing the right thing when writing to the >> GITS_BASER registers, and that writing a new value (with the valid bit >> set or not) should have an action of some sort on the fate of the >> existing mappings. > > I agree. I think whenever the GITS_BASERn or GITS_CBASER validity bit is > reset, we should empty the internal lists and assure the code does not > attempt to read the data structures in caches/RAM anymore. > I don't think that is likely to match the behavior suggested in the GIC/ITS spec. I doubt that hardware implementations will support software changing the BASERs without turning off the GIC, and therefore I don't think we'll see drivers doing this any time soon, and I don't think we need to support that. What I do think we should support is the ITS power management sequence pointed out in Section 6.6 in the spec. But I don't think this is urgent, as we don't seem to have any guests that power down and power up the ITS yet. Thanks, -Christoffer
