On Sun, Mar 12, 2023 at 01:22:40PM +0000, Marc Zyngier wrote: > On Tue, 07 Mar 2023 03:45:55 +0000, > Ricardo Koller <ricarkol@xxxxxxxxxx> wrote: > > > > From: Marc Zyngier <maz@xxxxxxxxxx> > > Thanks for writing a commit message for my hacks! > > > > > Broadcasted TLB invalidations (TLBI) are usually less performant than > > More precisely, TLBIs targeting the Inner Shareable domain. Also, > 's/broadcasted/broadcast/', as this is an adjective and not a verb > indicative of the past tense.. > > > their local variant. In particular, we observed some implementations > > non-shareable rather than local. 'Local' has all sort of odd > implementation specific meanings (local to *what* is the usual > question that follows...). > > > that take millliseconds to complete parallel broadcasted TLBIs. > > > > It's safe to use local, non-shareable, TLBIs when relaxing permissions > > s/local// > > > on a PTE in the KVM case for a couple of reasons. First, according to > > the ARM Arm (DDI 0487H.a D5-4913), permission relaxation does not need > > break-before-make. > > This requires some more details, and references to the latest revision > of the ARM ARM (0487I.a). In that particular revision, the relevant > information is contained in D8.13.1 "Using break-before-make when > updating translation table entries", and more importantly in the rule > R_WHZWS, which states that only a change of output address or block > size require a BBM. > > > Second, the VTTBR_EL2.CnP==0 case, where each PE > > has its own TLB entry for the same page, is tolerated correctly by KVM > > when doing permission relaxation. Not having changes broadcasted to > > all PEs is correct for this case, as it's safe to have other PEs fault > > on permission on the same page. > > I'm not sure mentioning CnP is relevant here. If CnP==1, the TLBI will > nuke the TLB visible by the sibling PE, but not any other. So this is > always a partial TLB invalidation, irrespective of CnP. > > Thanks, > > M. > Thanks Marc. Sent a new version incorporating all the above. Thanks, Ricardo > -- > Without deviation from the norm, progress is not possible.
