Like mentioned previously, having different mechanism for HS-mode and VS-mode to write HPMCOUNTER CSR is not acceptable. The “bypass-sbi” DT property only means that Linux PMU driver is now aware whether it is running natively or running
inside Guest/VM. This is totally hacky and won’t be acceptable.
Regards,
Anup
From: tech-privileged@... <tech-privileged@...>
On Behalf Of alankao Sent: 18 August 2020 15:17 To: tech-privileged@... Subject: Re: [RISC-V] [tech-privileged] A proposal to enhance RISC-V HPM (Hardware Performance Monitor)
Hi Anup,
We did the experiment based on our own settings and not yet consider the SBI extension proposal.
Please consider the approach in #278 with one additional condition: Any platform that supports configurations more than M-S-U should not provide a PMU with "bypass-sbi" attribute, like QEMU virt. Neither VS- nor HS- usage will be affected by this bit. Then,
you ask, what about emulating a platform that aims to only runs on M-S-U machines? Well, the one who ports the platform to QEMU/other simulators should put some warning message when the attempt to write happens, rather than implement the whole save-restore
just for the PMU status.
We don't need to add many CSRs. Just one bit in hpmevent*.
