Colton Lewis coltonlewis@google.com writes:
Marc Zyngier maz@kernel.org writes:
On Tue, 28 Jan 2025 22:08:27 +0000, Colton Lewis coltonlewis@google.com wrote:
- bitmap_set(cpu_pmu->cntr_mask, 0, pmcr_n);
- if (reserved_guest_counters > 0 && reserved_guest_counters <
pmcr_n) {
cpu_pmu->hpmn = reserved_guest_counters;cpu_pmu->partitioned = true;
Isn't this going to completely explode on a kernel running at EL1?
Trying to access an EL2 register at EL1 can do that. I'll add the appropriate hypercalls.
Ooohh. Making this work at EL1 is much more complicated than adding the hypercall to write MDCR because once HPMN takes effect, the upper range of counters that the host will use is only writable at EL2. That means using any register related to any counter in the upper range would also require a hypercall. The only way around that would be to avoid using this feature in the host entirely and only enable it when we load a guest.
I know we don't like feature discrepencies between VHE and nVHE mode, but Oliver thinks it might be justified here to have PMU partitioning be VHE-only.