Re: [PATCH v5 5/7] powerpc/mm: Write to PTCR only if ultravisor disabled

[Michael Ellerman <mpe@ellerman.id.au>]

Claudio Carvalho <cclaudio@linux.ibm.com> writes:
> In ultravisor enabled systems, PTCR becomes ultravisor privileged only
> for writing and an attempt to write to it will cause a Hypervisor
> Emulation Assitance interrupt.
>
> This patch adds the try_set_ptcr(val) macro as an accessor to
> mtspr(SPRN_PTCR, val), which will be executed only if ultravisor
> disabled.
>
> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> ---
>  arch/powerpc/include/asm/reg.h           | 13 +++++++++++++
>  arch/powerpc/mm/book3s64/hash_utils.c    |  4 ++--
>  arch/powerpc/mm/book3s64/pgtable.c       |  2 +-
>  arch/powerpc/mm/book3s64/radix_pgtable.c |  6 +++---
>  4 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index 10caa145f98b..14139b1ebdb8 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -15,6 +15,7 @@
>  #include <asm/cputable.h>
>  #include <asm/asm-const.h>
>  #include <asm/feature-fixups.h>
> +#include <asm/firmware.h>

reg.h is already too big and unwieldy.

Can you put this in ultravisor.h and include that in the appropriate places.

> @@ -1452,6 +1453,18 @@ static inline void update_power8_hid0(unsigned long hid0)
>  	 */
>  	asm volatile("sync; mtspr %0,%1; isync":: "i"(SPRN_HID0), "r"(hid0));
>  }
> +
> +/*
> + * In ultravisor enabled systems, PTCR becomes ultravisor privileged only for
> + * writing and an attempt to write to it will cause a Hypervisor Emulation
> + * Assistance interrupt.
> + */
> +#define try_set_ptcr(val)						\
> +	do {								\
> +		if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))	\
> +			mtspr(SPRN_PTCR, val);				\
> +	} while (0)

This should be a static inline please, not a macro.

Sorry, I don't like the name, we're not trying to set it, we know when
to set it and when not to.

It is awkward to come up with a good name because we don't have a term
for "hypervisor that's not running under an ultravisor".

Maybe set_ptcr_when_no_uv()

Which is kinda messy, someone feel free to come up with something
better.

I also see some more accesses to the PTCR in
arch/powerpc/platforms/powernv/idle.c which you haven't patched?

cheers