Re: [PATCH v4 07/15] x86/paravirt: switch time pvops functions to use static_call()

[Borislav Petkov]

On Wed, Jan 20, 2021 at 02:55:47PM +0100, Juergen Gross wrote:
> The time pvops functions are the only ones left which might be
> used in 32-bit mode and which return a 64-bit value.
> 
> Switch them to use the static_call() mechanism instead of pvops, as
> this allows quite some simplification of the pvops implementation.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V4:
> - drop paravirt_time.h again
> - don't move Hyper-V code (Michael Kelley)
> ---
>  arch/x86/Kconfig                      |  1 +
>  arch/x86/include/asm/mshyperv.h       |  2 +-
>  arch/x86/include/asm/paravirt.h       | 17 ++++++++++++++---
>  arch/x86/include/asm/paravirt_types.h |  6 ------
>  arch/x86/kernel/cpu/vmware.c          |  5 +++--
>  arch/x86/kernel/kvm.c                 |  2 +-
>  arch/x86/kernel/kvmclock.c            |  2 +-
>  arch/x86/kernel/paravirt.c            | 16 ++++++++++++----
>  arch/x86/kernel/tsc.c                 |  2 +-
>  arch/x86/xen/time.c                   | 11 ++++-------
>  drivers/clocksource/hyperv_timer.c    |  5 +++--
>  drivers/xen/time.c                    |  2 +-
>  12 files changed, 42 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 21f851179ff0..7ccd4a80788c 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -771,6 +771,7 @@ if HYPERVISOR_GUEST
>  
>  config PARAVIRT
>  	bool "Enable paravirtualization code"
> +	depends on HAVE_STATIC_CALL
>  	help
>  	  This changes the kernel so it can modify itself when it is run
>  	  under a hypervisor, potentially improving performance significantly
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 30f76b966857..b4ee331d29a7 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -63,7 +63,7 @@ typedef int (*hyperv_fill_flush_list_func)(
>  static __always_inline void hv_setup_sched_clock(void *sched_clock)
>  {
>  #ifdef CONFIG_PARAVIRT
> -	pv_ops.time.sched_clock = sched_clock;
> +	paravirt_set_sched_clock(sched_clock);
>  #endif
>  }
>  
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 4abf110e2243..1e45b46fae84 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -15,11 +15,22 @@
>  #include <linux/bug.h>
>  #include <linux/types.h>
>  #include <linux/cpumask.h>
> +#include <linux/static_call_types.h>
>  #include <asm/frame.h>
>  
> -static inline unsigned long long paravirt_sched_clock(void)
> +u64 dummy_steal_clock(int cpu);
> +u64 dummy_sched_clock(void);
> +
> +DECLARE_STATIC_CALL(pv_steal_clock, dummy_steal_clock);
> +DECLARE_STATIC_CALL(pv_sched_clock, dummy_sched_clock);

Did you build this before sending?

I'm test-applying this on rc6 + tip/master so I probably am using a
different tree so it looks like something has changed in the meantime.
-rc6 has a couple of Xen changes which made applying those to need some
wiggling in...

Maybe you should redo them ontop of tip/master. That is, *if* they're
going to eventually go through tip. The diffstat has Xen stuff too so we
might need some synchronization here what goes where how...

./arch/x86/include/asm/paravirt.h:24:1: warning: data definition has no type or storage class
   24 | DECLARE_STATIC_CALL(pv_steal_clock, dummy_steal_clock);
      | ^~~~~~~~~~~~~~~~~~~
./arch/x86/include/asm/paravirt.h:24:1: error: type defaults to ‘int’ in declaration of ‘DECLARE_STATIC_CALL’ [-Werror=implicit-int]
./arch/x86/include/asm/paravirt.h:24:1: warning: parameter names (without types) in function declaration
./arch/x86/include/asm/paravirt.h:25:1: warning: data definition has no type or storage class
   25 | DECLARE_STATIC_CALL(pv_sched_clock, dummy_sched_clock);
      | ^~~~~~~~~~~~~~~~~~~
./arch/x86/include/asm/paravirt.h:25:1: error: type defaults to ‘int’ in declaration of ‘DECLARE_STATIC_CALL’ [-Werror=implicit-int]
./arch/x86/include/asm/paravirt.h:25:1: warning: parameter names (without types) in function declaration
./arch/x86/include/asm/paravirt.h: In function ‘paravirt_sched_clock’:
./arch/x86/include/asm/paravirt.h:33:9: error: implicit declaration of function ‘static_call’ [-Werror=implicit-function-declaration]
   33 |  return static_call(pv_sched_clock)();
      |         ^~~~~~~~~~~
./arch/x86/include/asm/paravirt.h:33:21: error: ‘pv_sched_clock’ undeclared (first use in this function); did you mean ‘dummy_sched_clock’?
   33 |  return static_call(pv_sched_clock)();
      |                     ^~~~~~~~~~~~~~
      |                     dummy_sched_clock
./arch/x86/include/asm/paravirt.h:33:21: note: each undeclared identifier is reported only once for each function it appears in
./arch/x86/include/asm/paravirt.h: In function ‘paravirt_steal_clock’:
./arch/x86/include/asm/paravirt.h:47:21: error: ‘pv_steal_clock’ undeclared (first use in this function); did you mean ‘dummy_steal_clock’?
   47 |  return static_call(pv_steal_clock)(cpu);
      |                     ^~~~~~~~~~~~~~
      |                     dummy_steal_clock
cc1: some warnings being treated as errors
make[1]: *** [scripts/Makefile.build:117: arch/x86/kernel/asm-offsets.s] Error 1
make: *** [Makefile:1200: prepare0] Error 2

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette