[Xen-devel] Re: [PATCH 2/9] xen: hook io_apic read/write operations

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Yinghai Lu wrote:
> Jeremy Fitzhardinge wrote:
>   
> > In Xen, writes to the IO APIC are paravirtualized via hypercalls, so
> > implement the appropriate operations.
> >
> > This version of the patch just hooks the io_apic read/write functions
> > directly, rather than introducing another layer of indirection.  The
> > xen_initial_domain() tests compile to 0 if CONFIG_XEN_DOM0 isn't set,
> > and are cheap if it is.
> >
> > (An alternative would be to add io_apic_ops, and point them to the Xen
> > implementation as needed.  HPA deemed this extra level of indirection to
> > be excessive.)
> >     
> that will be more clean.
>   
That was my thought too.


> > Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> > ---
> >  arch/x86/include/asm/io_apic.h |    6 ++++
> >  arch/x86/kernel/io_apic.c      |   32 ++++++++++++++++++++--
> >  arch/x86/xen/Makefile          |    3 +-
> >  arch/x86/xen/apic.c            |   57 ++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/xen/enlighten.c       |    2 +
> >  arch/x86/xen/xen-ops.h         |    6 ++++
> >  6 files changed, 102 insertions(+), 4 deletions(-)
> >  create mode 100644 arch/x86/xen/apic.c
> >
> > diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
> > index 59cb4a1..20b543a 100644
> > --- a/arch/x86/include/asm/io_apic.h
> > +++ b/arch/x86/include/asm/io_apic.h
> > @@ -183,4 +183,10 @@ static inline void ioapic_init_mappings(void)      { }
> >  static inline void probe_nr_irqs_gsi(void)     { }
> >  #endif
> >  
> > +void xen_io_apic_init(void);
> > +unsigned int xen_io_apic_read(unsigned apic, unsigned reg);
> > +void xen_io_apic_write(unsigned int apic,
> > +                      unsigned int reg, unsigned int value);
> > +
> > +
> >  #endif /* _ASM_X86_IO_APIC_H */
> > diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
> > index 7248ca1..de0368a 100644
> > --- a/arch/x86/kernel/io_apic.c
> > +++ b/arch/x86/kernel/io_apic.c
> > @@ -62,6 +62,8 @@
> >  #include <asm/uv/uv_hub.h>
> >  #include <asm/uv/uv_irq.h>
> >  
> > +#include <asm/xen/hypervisor.h>
> > +
> >  #include <asm/genapic.h>
> >  
> >  #define __apicdebuginit(type) static type __init
> > @@ -399,14 +401,26 @@ static __attribute_const__ struct io_apic __iomem 
> > *io_apic_base(int idx)
> >  
> >  static inline unsigned int io_apic_read(unsigned int apic, unsigned int reg)
> >  {
> > -       struct io_apic __iomem *io_apic = io_apic_base(apic);
> > +       struct io_apic __iomem *io_apic;
> > +
> > +       if (xen_initial_domain())
> > +               return xen_io_apic_read(apic, reg);
> >     
> you may have _xen_io_apic_read(apic, reg);
> and xen_io_apic_read(apic, reg) will call xen_initial_domain internally.
>   
How would that work?  What would it return in the xen/non-xen states to 
indicate that the normal read operation should be performed?  I don't 
think it would be any clearer.
> or sth like
> extra if (io_apic_ops)
>         io_apic->read()...
>   
I think if there were an _ops structure, it should just go though it 
unconditionally.
   J


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