Re: [PATCH 1/3] arm/arm64/xen: use C inlines for privcmd_call

Russell King - ARM Linux admin
2019-11-22T00:23:27Z

On Thu, Nov 21, 2019 at 01:48:03PM -0500, Pavel Tatashin wrote:
> privcmd_call requires to enable access to userspace for the
> duration of the hypercall.
>
> Currently, this is done via assembly macros. Change it to C
> inlines instead.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> ---
> arch/arm/include/asm/assembler.h | 2 +-
> arch/arm/include/asm/uaccess.h | 32 ++++++++++++++++++++++++++------
> arch/arm/xen/enlighten.c | 2 +-
> arch/arm/xen/hypercall.S | 15 ++-------------
> arch/arm64/xen/hypercall.S | 19 ++-----------------
> include/xen/arm/hypercall.h | 23 ++++++++++++++++++++---
> 6 files changed, 52 insertions(+), 41 deletions(-)
>
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index 99929122dad7..8e9262a0f016 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -480,7 +480,7 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
> .macro uaccess_disable, tmp, isb=1
> #ifdef CONFIG_CPU_SW_DOMAIN_PAN
> /*
> - * Whenever we re-enter userspace, the domains should always be
> + * Whenever we re-enter kernel, the domains should always be
> * set appropriately.
> */
> mov \tmp, #DACR_UACCESS_DISABLE
> diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
> index 98c6b91be4a8..79d4efa3eb62 100644
> --- a/arch/arm/include/asm/uaccess.h
> +++ b/arch/arm/include/asm/uaccess.h
> @@ -16,6 +16,23 @@
>
> #include <asm/extable.h>
>
> +#ifdef CONFIG_CPU_SW_DOMAIN_PAN
> +static __always_inline void uaccess_enable(void)
> +{
> + unsigned long val = DACR_UACCESS_ENABLE;
> +
> + asm volatile("mcr p15, 0, %0, c3, c0, 0" : : "r" (val));
> + isb();
> +}
> +
> +static __always_inline void uaccess_disable(void)
> +{
> + unsigned long val = DACR_UACCESS_ENABLE;
> +
> + asm volatile("mcr p15, 0, %0, c3, c0, 0" : : "r" (val));
> + isb();
> +}

Rather than inventing these, why not use uaccess_save_and_enable()..
uaccess_restore() around the Xen call?

--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up