[TF-A] Advisory TFV 5 to CVE-2017-15031 only saves/stores the PMCR_EL0 across world switching

Hi David/ATF Support,

An excerpt from the commit message to CVE-2017-15031 is "Additionally, PMCR_EL0 is added to the list of registers that are saved and restored during a world switch."

My question is why it is only being saved/restored across the world switch and not during a "normal" SMC call? When I do modify the PMCR_EL0 in EL2 or NonSecure-EL1 and run the smc call the PMCCNTR counter counts during the smc call and does expose secure world timing information to NonSecure in that matter.

Thanks, Marek