linux-kernel - Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1334925508.28331.63.camel@zakaz.uk.xensource.com>
Date:	Fri, 20 Apr 2012 13:38:28 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Lin Ming <mlin@...pku.edu.cn>
CC:	Andrew Cooper <Andrew.Cooper3@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with
 hypercall

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@...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? Would a BUG_ON be
appropriate/

> unsigned int ret = apic_read(...);
> if (ret == -1)
> 	//handle error.
> 
> Thanks,
> Lin Ming
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/