On 13/06/18 11:35, Will Deacon wrote: > On Tue, Jun 12, 2018 at 04:41:32PM -0400, Agustin Vega-Frias wrote: >> Hi Mark, >> >> On 2018-06-12 10:40, Mark Rutland wrote: >>> Hi, >>> >>> On Thu, Jun 07, 2018 at 09:56:48AM -0400, Agustin Vega-Frias wrote: >>>> Selection of these events can be envisioned as indexing them from >>>> a 3D matrix: >>>> - the first index selects a Region Event Selection Register >>>> (PMRESRx_EL0) >>>> - the second index selects a group from which only one event at a time >>>> can be selected >>>> - the third index selects the event >>>> >>>> The event is encoded into perf_event_attr.config as 0xPRCCG, where: >>>> P [config:16 ] = prefix (flag that indicates a matrix-based >>>> event) >>>> R [config:12-15] = register (specifies the PMRESRx_EL0 instance) >>>> G [config:0-3 ] = group (specifies the event group) >>>> CC [config:4-11 ] = code (specifies the event) >>>> >>>> Events with the P flag set to zero are treated as common PMUv3 events >>>> and are directly programmed into PMXEVTYPERx_EL0. >>>> >>>> The first two indexes are set combining the RESR and group number with >>>> a base number and writing it into the architected PMXEVTYPER_EL0 >>>> register. >>>> The third index is set by writing the code into the bits corresponding >>>> with the group into the appropriate IMPLEMENTATION DEFINED PMRESRx_EL0 >>>> register. >>> >>> When are the IMP DEF registers accessible at EL0? Are those goverend by >>> the same controls as the architected registers? >> >> No, there is a separate IMP DEF register to control access. > > Great :( We need to make sure we disable EL0 access during boot then, but > that means we need to prove for the existence of this thing in head.S > (since the PMU driver might not get loaded). > > Also, what's the kvm story here so that we don't accidentally open up a > VM-VM side-channel via these registers? How do the EL1 trapping controls > work?
We'd trap the IMPDEF register access and inject an UNDEF (assuming that the IMPDEF trapping works correctly). I have strictly no plan to support this in a guest. Thanks, M. -- Jazz is not dead. It just smells funny...