On Tue, 25 Jan 2022 12:25:47 +0000, Mark Brown broonie@kernel.org wrote:
[1 <text/plain; us-ascii (7bit)>] On Tue, Jan 25, 2022 at 11:27:55AM +0000, Marc Zyngier wrote:
Mark Brown broonie@kernel.org wrote:
- if (IS_ENABLED(CONFIG_ARM64_SME) && cpus_have_final_cap(ARM64_SME))
Please drop the IS_ENABLED(). We purposely avoid conditional compilation in KVM in order to avoid bitrot, and the amount of code you save isn't significant. Having a static key is more than enough to avoid runtime costs.
Sure, I wanted to be extra careful here as this is all in hot paths and going to get moved elsewhere when we have real guest support.
- if (IS_ENABLED(CONFIG_ARM64_SME) && cpus_have_final_cap(ARM64_SME) &&
cpus_have_final_cap(ARM64_HAS_FGT)) {val = read_sysreg_s(SYS_HFGRTR_EL2);val &= ~(HFGxTR_EL2_nTPIDR_EL0_MASK |HFGxTR_EL2_nSMPRI_EL1_MASK);write_sysreg_s(val, SYS_HFGRTR_EL2);val = read_sysreg_s(SYS_HFGWTR_EL2);val &= ~(HFGxTR_EL2_nTPIDR_EL0_MASK |HFGxTR_EL2_nSMPRI_EL1_MASK);write_sysreg_s(val, SYS_HFGWTR_EL2);- }
If the CPUs do not have FGT, what provides the equivalent trapping?
Nothing for nVHE mode.
That's what I feared.
If FGT is mandatory when SME exists, then you should simplify the condition.
OK, I'll remove the defensiveness here. FGT is mandatory from v8.6 and SME is a v9 feature so people shouldn't build a SME implementation that lacks FGT.
Can you then please make it that SME doesn't get enabled at all if FGT isn't present? It would also be good to have a clarification in the architecture that it isn't allowed to build SME without FGT (specially given that v9.0 is congruent to v8.5, and thus doesn't have FGT).
Thanks,
M.