[PATCH 00/15] arm64/kvm: use common sysreg definitions

Will Deacon will.deacon at arm.com
Fri Mar 10 10:35:55 PST 2017

On Fri, Mar 10, 2017 at 08:17:22AM +0000, Marc Zyngier wrote:
> On Thu, Mar 09 2017 at  5:07:12 pm GMT, Mark Rutland <mark.rutland at arm.com> wrote:
> > Currently we duplicate effort in maintaining system register encodings across
> > arm64's <asm/sysreg.h>, KVM's sysreg tables, and other places. This redundancy
> > is unfortunate, and as encodings are encoded in-place without any mnemonic,
> > this ends up more painful to read than necessary.
> >
> > This series ameliorates this by making <asm/sysreg.h> the canonical location
> > for (architected) system register encodings, with other users building atop of
> > this, e.g. with KVM deriving its sysreg table values from the common mnemonics.
> >
> > I've only attacked AArch64-native SYS encodings, and ignored CP{15,14}
> > registers for now, but these could be handled similarly. Largely, I've stuck to
> > only what KVM needs, though for the debug and perfmon groups it was easier to
> > take the whole group from the ARM ARM than to filter them to only what KVM
> > needed today.
> >
> > To verify that I haven't accidentally broken KVM, I've diffed sys_regs.o and
> > sys_regs_generic_v8.o on a section-by-section basis before and after the series
> > is applied. The .text, .data, and .rodata sections (and most others) are
> > identical. The __bug_table section, and some .debug* sections differ, and this
> > appears to be due to line numbers changing due to removed lines.
> >
> > One thing I wasn't sure how to address was banks of registers such as
> > PMEVCNTR<n>_EL0. We currently enumerate all cases for our GICv3 definitions,
> > but it seemed painful to expand ~30 cases for PMEVCNTR<n>_EL0 and friends, and
> > for these I've made the macros take an 'n' parameter. It would be nice to be
> > consistent either way, and I'm happy to expand those cases.
> >
> > I've pushed thes series out to a branch [1] based on v4.11-rc1. It looks like
> > git rebase is also happy to apply the patches atop of the kvm-arm-for-4.11-rc2
> > tag.
> I had a quick glance at this series, and this looks like a very good
> piece of work - thanks for doing this.
> The next question is how do we merge this. Obviously, we can't split it
> between trees, and this is very likely to clash with anything that we
> will merge on the KVM side (the sysreg table is a popular place).
> Will, Catalin: Would it make sense to create a stable branch with these
> patches, and merge it into both the arm64 and KVM trees? That'd make
> things easier...

I think the scope for conflict on our side is pretty high too, so a shared
branch might be the best way to go. I don't want to branch just yet though,
so I'll probably wait a week or so before setting something in stone.


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