On Sun, Mar 20, 2016 at 10:07:04PM +0100, Christoffer Dall wrote:
> On Fri, Mar 18, 2016 at 06:07:09PM +0000, Catalin Marinas wrote:
> > On Fri, Mar 18, 2016 at 05:25:59PM +0000, Marc Zyngier wrote:
> > > When running with VHE, there is no need to translate kernel pointers
> > > to the EL2 memory space, since we're already there (and we have a much
> > > saner memory map to start with).
> > >
> > > Unfortunately, kvm_ksym_ref is getting in the way, and the first
> > > call into the "hypervisor" section is going to end up in fireworks,
> > > since we're now branching into nowhereland. Meh.
> > >
> > > A potential solution is to test if VHE is engaged or not, and only
> > > perform the translation in the negative case. With this in place,
> > > VHE is able to run again.
> > >
> > > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> > > ---
> > > arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
> > > 1 file changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > > index 226f49d..282f907 100644
> > > --- a/arch/arm64/include/asm/kvm_asm.h
> > > +++ b/arch/arm64/include/asm/kvm_asm.h
> > > @@ -26,7 +26,13 @@
> > > #define KVM_ARM64_DEBUG_DIRTY_SHIFT 0
> > > #define KVM_ARM64_DEBUG_DIRTY (1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)
> > >
> > > -#define kvm_ksym_ref(sym) phys_to_virt((u64)&sym - kimage_voffset)
> > > +#define kvm_ksym_ref(sym) \
> > > + ({ \
> > > + void *val = sym; \
> >
> > Should we not use &sym, for consistency and just in case we ever pass
> > something other than a function.
>
> we already do, we pass the symbox for an extern char _foo[] array, but
> that should work just the same with sym and &sym.
Just for consistency between "val = sym" and "phys_to_virt((u64)&sym..."
> Given the effort put in to avoid these kinds of branches for the VHE
> code, it may be worth optimizing this later on with the use of
> instruction patching or static keys to avoid the branch on every vm
> entry/exit?
Marc tried with run-time patching first but the code was still reading
kimage_voffset even with VHE. Anyway, it can be optimised later.
> > > + if (!is_kernel_in_hyp_mode()) \
> > > + val = phys_to_virt((u64)&sym - kimage_voffset); \
> > > + val; \
> > > + })
> >
> > Otherwise:
> >
> > Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
>
> Thanks, I can change to &sym and queue this patch (not assuming you plan
> on taking it directly via the arm64 tree).
Please feel free to merge this via the kvm tree.
--
Catalin
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