Re: A proposal to enhance RISC-V HPM (Hardware Performance Monitor)
I think I am repeating myself here but still don’t see any benefit of allowing HPMCOUNTER CSR write access to S-mode. On the contrary, it will make context switching expensive for hypervisors.
The SBI PMU extension is designed such that kernel need not be aware of HS-mode or VS-mode. For Guest kernel (VS-mode), SBI is provided by Hypervisor so Hypervisor will act as mediator for Guest kernel. For Host kernel (HS-mode), SBI provider is M-mode runtime firmware (OpenSBI). The Linux PMU driver should not
care which mode it is running (HS-mode or VS-mode). The same rationale applies here, we use single Linux RISC-V kernel image for both Guest and Host.
From: tech-privileged@... <tech-privileged@...> On Behalf Of alankao
Sent: 05 August 2020 10:23
Subject: Re: [RISC-V] [tech-privileged] A proposal to enhance RISC-V HPM (Hardware Performance Monitor)