On Fri, Jun 21, 2024 at 04:52:09PM +0200, Andrew Jones wrote: > On Fri, Jun 21, 2024 at 03:04:47PM GMT, Conor Dooley wrote: > > On Fri, Jun 21, 2024 at 03:15:10PM +0200, Andrew Jones wrote: > > > On Fri, Jun 21, 2024 at 02:42:15PM GMT, Alexandre Ghiti wrote: > > > I understand the concern; old SBI implementations will leave svadu in the > > > DT but not actually enable it. Then, since svade may not be in the DT if > > > the platform doesn't support it or it was left out on purpose, Linux will > > > only see svadu and get unexpected exceptions. This is something we could > > > force easily with QEMU and an SBI implementation which doesn't do anything > > > for svadu. I hope vendors of real platforms, which typically provide their > > > own firmware and DTs, would get this right, though, especially since Linux > > > should fail fast in their testing when they get it wrong. > > > > I'll admit, I wasn't really thinking here about something like QEMU that > > puts extensions into the dtb before their exact meanings are decided > > upon. I almost only ever think about "real" systems, and in those cases > > I would expect that if you can update the representation of the hardware > > provided to (or by the firmware to Linux) with new properties, then updating > > the firmware itself should be possible. > > > > Does QEMU have the this exact problem at the moment? I know it puts > > Svadu in the max cpu, but does it enable the behaviour by default, even > > without the SBI implementation asking for it? > > Yes, because QEMU has done hardware A/D updating since it first started > supporting riscv, which means it did svadu when neither svadu nor svade > were in the DT. The "fix" for that was to ensure we have svadu and !svade > by default, which means we've perfectly realized Alexandre's concern... > We should be able to change the named cpu types that don't support svadu > to only have svade in their DTs, since that would actually be fixing those > cpu types, but we'll need to discuss how to proceed with the generic cpu > types like 'max'. Correct me please, since I think I am misunderstanding: At the moment QEMU does A/D updating whether or not the SBI implantation asks for it, with the max CPU. The SBI implementation doesn't understand Svadu and won't strip it. The kernel will get a DT with Svadu in it, but Svadu will be enabled, so it is not a problem.
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