Messages in this thread | | | Date | Fri, 20 Apr 2012 13:52:19 +0100 | From | "Jan Beulich" <> | Subject | Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall |
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>>> On 20.04.12 at 14:38, Ian Campbell <Ian.Campbell@citrix.com> wrote: > On Fri, 2012-04-20 at 12:13 +0100, Lin Ming wrote: >> On Fri, 2012-04-20 at 10:58 +0100, Andrew Cooper wrote: >> > On 20/04/12 10:25, Lin Ming wrote: >> > > Implements xen_io_apic_read with hypercall, so it returns proper IO-APIC >> > > information instead of fabricated one. >> > > >> > > Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn> >> > > --- >> > > arch/x86/xen/apic.c | 16 +++++++++++----- >> > > 1 files changed, 11 insertions(+), 5 deletions(-) >> > > >> > > diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c >> > > index aee16ab..f1f392d 100644 >> > > --- a/arch/x86/xen/apic.c >> > > +++ b/arch/x86/xen/apic.c >> > > @@ -1,14 +1,20 @@ >> > > #include <linux/init.h> >> > > #include <asm/x86_init.h> >> > > +#include <asm/apic.h> >> > > +#include <xen/interface/physdev.h> >> > > +#include <asm/xen/hypercall.h> >> > > >> > > unsigned int xen_io_apic_read(unsigned apic, unsigned reg) >> > > { >> > > - if (reg == 0x1) >> > > - return 0x00170020; >> > > - else if (reg == 0x0) >> > > - return apic << 24; >> > > + struct physdev_apic apic_op; >> > > + int ret; >> > > >> > > - return 0xff; >> > > + apic_op.apic_physbase = mpc_ioapic_addr(apic); >> > > + apic_op.reg = reg; >> > > + ret = HYPERVISOR_physdev_op(PHYSDEVOP_apic_read, &apic_op); >> > > + if (ret) >> > > + return ret; >> > > + return apic_op.value; >> > >> > Hypercall ret errors are negative, yet this function is unsigned. Given >> > that the previous function had no possible way to fail, perhaps on error >> > you should fake up the values as before. >> >> How about return -1 on error? >> The calling function can check -1 for error. > > Isn't -1 potentially (at least theoretically) a valid value to read from > one of these registers? > > Under what circumstances can these hypercalls fail?
Only when the input is wrong (or it's not a privileged domain).
> Would a BUG_ON be appropriate/
Probably.
Jan
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