[PATCH] xen: fix logical error in tlb flushing

[PATCH] xen: fix logical error in tlb flushing

[Alex Shi]

While TLB_FLUSH_ALL gets passed as 'end' argument to
flush_tlb_others(), the Xen code was made to check its 'start'
parameter. That may give a incorrect op.cmd to MMUEXT_INVLPG_MULTI
instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page can not
be flushed from TLB.

This patch fixed this issue.

Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Alex Shi <alex.shi@intel.com>
---
 arch/x86/xen/mmu.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index b65a761..5141d80 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1283,7 +1283,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
 	cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));
 
 	args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
-	if (start != TLB_FLUSH_ALL && (end - start) <= PAGE_SIZE) {
+	if (end != TLB_FLUSH_ALL && (end - start) <= PAGE_SIZE) {
 		args->op.cmd = MMUEXT_INVLPG_MULTI;
 		args->op.arg1.linear_addr = start;
 	}
-- 
1.7.5.4

Re: [PATCH] xen: fix logical error in tlb flushing

[Jan Beulich]

>>> On 24.08.12 at 10:55, Alex Shi <alex.shi@intel.com> wrote:
> While TLB_FLUSH_ALL gets passed as 'end' argument to
> flush_tlb_others(), the Xen code was made to check its 'start'
> parameter. That may give a incorrect op.cmd to MMUEXT_INVLPG_MULTI
> instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page can not
> be flushed from TLB.
> 
> This patch fixed this issue.
> 
> Reported-by: Jan Beulich <jbeulich@suse.com>
> Signed-off-by: Alex Shi <alex.shi@intel.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

> ---
>  arch/x86/xen/mmu.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index b65a761..5141d80 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1283,7 +1283,7 @@ static void xen_flush_tlb_others(const struct cpumask 
> *cpus,
>  	cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));
>  
>  	args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
> -	if (start != TLB_FLUSH_ALL && (end - start) <= PAGE_SIZE) {
> +	if (end != TLB_FLUSH_ALL && (end - start) <= PAGE_SIZE) {
>  		args->op.cmd = MMUEXT_INVLPG_MULTI;
>  		args->op.arg1.linear_addr = start;
>  	}
> -- 
> 1.7.5.4
> 
> .

Re: [PATCH] xen: fix logical error in tlb flushing

[Konrad Rzeszutek Wilk]

On Fri, Aug 24, 2012 at 04:16:39PM +0100, Jan Beulich wrote:
> >>> On 24.08.12 at 10:55, Alex Shi <alex.shi@intel.com> wrote:
> > While TLB_FLUSH_ALL gets passed as 'end' argument to
> > flush_tlb_others(), the Xen code was made to check its 'start'
> > parameter. That may give a incorrect op.cmd to MMUEXT_INVLPG_MULTI
> > instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page can not
> > be flushed from TLB.
> > 
> > This patch fixed this issue.
> > 
> > Reported-by: Jan Beulich <jbeulich@suse.com>
> > Signed-off-by: Alex Shi <alex.shi@intel.com>
> 
> Acked-by: Jan Beulich <jbeulich@suse.com>

How can I reproduce this and should this also go to stable@kernel.org?
> 
> > ---
> >  arch/x86/xen/mmu.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> > index b65a761..5141d80 100644
> > --- a/arch/x86/xen/mmu.c
> > +++ b/arch/x86/xen/mmu.c
> > @@ -1283,7 +1283,7 @@ static void xen_flush_tlb_others(const struct cpumask 
> > *cpus,
> >  	cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));
> >  
> >  	args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
> > -	if (start != TLB_FLUSH_ALL && (end - start) <= PAGE_SIZE) {
> > +	if (end != TLB_FLUSH_ALL && (end - start) <= PAGE_SIZE) {
> >  		args->op.cmd = MMUEXT_INVLPG_MULTI;
> >  		args->op.arg1.linear_addr = start;
> >  	}
> > -- 
> > 1.7.5.4
> > 
> > .
> 
> 
> 

Re: [PATCH] xen: fix logical error in tlb flushing

[Jan Beulich]

>>> On 24.08.12 at 20:17, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> On Fri, Aug 24, 2012 at 04:16:39PM +0100, Jan Beulich wrote:
>> >>> On 24.08.12 at 10:55, Alex Shi <alex.shi@intel.com> wrote:
>> > While TLB_FLUSH_ALL gets passed as 'end' argument to
>> > flush_tlb_others(), the Xen code was made to check its 'start'
>> > parameter. That may give a incorrect op.cmd to MMUEXT_INVLPG_MULTI
>> > instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page can not
>> > be flushed from TLB.
>> > 
>> > This patch fixed this issue.
>> > 
>> > Reported-by: Jan Beulich <jbeulich@suse.com>
>> > Signed-off-by: Alex Shi <alex.shi@intel.com>
>> 
>> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
> How can I reproduce this

I don't know, I spotted this while looking at the code.

> and should this also go to stable@kernel.org?

No, the problem got introduced in 3.6-rc1.

Jan

Re: [PATCH] xen: fix logical error in tlb flushing

[Alex Shi]

On 08/25/2012 03:45 AM, Jan Beulich wrote:

>>>> On 24.08.12 at 20:17, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
>> On Fri, Aug 24, 2012 at 04:16:39PM +0100, Jan Beulich wrote:
>>>>>> On 24.08.12 at 10:55, Alex Shi <alex.shi@intel.com> wrote:
>>>> While TLB_FLUSH_ALL gets passed as 'end' argument to
>>>> flush_tlb_others(), the Xen code was made to check its 'start'
>>>> parameter. That may give a incorrect op.cmd to MMUEXT_INVLPG_MULTI
>>>> instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page can not
>>>> be flushed from TLB.
>>>>
>>>> This patch fixed this issue.
>>>>
>>>> Reported-by: Jan Beulich <jbeulich@suse.com>
>>>> Signed-off-by: Alex Shi <alex.shi@intel.com>
>>>
>>> Acked-by: Jan Beulich <jbeulich@suse.com>



CC to Yongjie,
Could you like to test this patch on PV guest

>>
>> How can I reproduce this

>

> I don't know, I spotted this while looking at the code.


Again, since the old buggy code doesn't cause trouble in PV guest, guess
the hypercall for MMUEXT_INVLPG_MULTI was translated or treated as
MMUEXT_TLB_FLUSH_MULTI. If so, believe correct this will bring a big
performance benefit.

RE: [PATCH] xen: fix logical error in tlb flushing

[Ren, Yongjie]

> -----Original Message-----
> From: Shi, Alex
> Sent: Wednesday, September 05, 2012 1:35 PM
> To: Jan Beulich
> Cc: Konrad Rzeszutek Wilk; tglx@linutronix.de; mingo@redhat.com;
> linux-kernel@vger.kernel.org; hpa@zytor.com; Ren, Yongjie
> Subject: Re: [PATCH] xen: fix logical error in tlb flushing
> 
> On 08/25/2012 03:45 AM, Jan Beulich wrote:
> 
> >>>> On 24.08.12 at 20:17, Konrad Rzeszutek Wilk
> <konrad.wilk@oracle.com> wrote:
> >> On Fri, Aug 24, 2012 at 04:16:39PM +0100, Jan Beulich wrote:
> >>>>>> On 24.08.12 at 10:55, Alex Shi <alex.shi@intel.com> wrote:
> >>>> While TLB_FLUSH_ALL gets passed as 'end' argument to
> >>>> flush_tlb_others(), the Xen code was made to check its 'start'
> >>>> parameter. That may give a incorrect op.cmd to
> MMUEXT_INVLPG_MULTI
> >>>> instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page
> can not
> >>>> be flushed from TLB.
> >>>>
> >>>> This patch fixed this issue.
> >>>>
> >>>> Reported-by: Jan Beulich <jbeulich@suse.com>
> >>>> Signed-off-by: Alex Shi <alex.shi@intel.com>
> >>>
> >>> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
Tested-by: Yongjie Ren <yongjie.ren@intel.com>

> 
> CC to Yongjie,
> Could you like to test this patch on PV guest
> 
Xen Dom0 and a PV guest kernel with this patch can boot up correctly.

Re: [PATCH] xen: fix logical error in tlb flushing

[Jan Beulich]

>>> On 05.09.12 at 07:34, Alex Shi <alex.shi@intel.com> wrote:
> On 08/25/2012 03:45 AM, Jan Beulich wrote:
>>>>> On 24.08.12 at 20:17, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
>>> How can I reproduce this
>>
>> I don't know, I spotted this while looking at the code.
> 
> Again, since the old buggy code doesn't cause trouble in PV guest, guess
> the hypercall for MMUEXT_INVLPG_MULTI was translated or treated as
> MMUEXT_TLB_FLUSH_MULTI. If so, believe correct this will bring a big
> performance benefit.

It's not clear to me what was buggy with the code prior to your
change. And no, there's no magic widening of the scope of these
MMU operations - if you ask the hypervisor for a single page
invalidation, that's what it's going to do. But of course, there
are cases where extra (full) invalidations need to be done
without a guest asking for them. But that's nothing a guest can
validly make itself dependent upon.

Jan

Re: [PATCH] xen: fix logical error in tlb flushing

[Konrad Rzeszutek Wilk]

On Wed, Sep 05, 2012 at 05:41:37AM +0000, Ren, Yongjie wrote:
> > -----Original Message-----
> > From: Shi, Alex
> > Sent: Wednesday, September 05, 2012 1:35 PM
> > To: Jan Beulich
> > Cc: Konrad Rzeszutek Wilk; tglx@linutronix.de; mingo@redhat.com;
> > linux-kernel@vger.kernel.org; hpa@zytor.com; Ren, Yongjie
> > Subject: Re: [PATCH] xen: fix logical error in tlb flushing
> > 
> > On 08/25/2012 03:45 AM, Jan Beulich wrote:
> > 
> > >>>> On 24.08.12 at 20:17, Konrad Rzeszutek Wilk
> > <konrad.wilk@oracle.com> wrote:
> > >> On Fri, Aug 24, 2012 at 04:16:39PM +0100, Jan Beulich wrote:
> > >>>>>> On 24.08.12 at 10:55, Alex Shi <alex.shi@intel.com> wrote:
> > >>>> While TLB_FLUSH_ALL gets passed as 'end' argument to
> > >>>> flush_tlb_others(), the Xen code was made to check its 'start'
> > >>>> parameter. That may give a incorrect op.cmd to
> > MMUEXT_INVLPG_MULTI
> > >>>> instead of MMUEXT_TLB_FLUSH_MULTI. Then it causes some page
> > can not
> > >>>> be flushed from TLB.
> > >>>>
> > >>>> This patch fixed this issue.
> > >>>>
> > >>>> Reported-by: Jan Beulich <jbeulich@suse.com>
> > >>>> Signed-off-by: Alex Shi <alex.shi@intel.com>
> > >>>
> > >>> Acked-by: Jan Beulich <jbeulich@suse.com>
> > 
> Tested-by: Yongjie Ren <yongjie.ren@intel.com>
> 
> > 
> > CC to Yongjie,
> > Could you like to test this patch on PV guest
> > 
> Xen Dom0 and a PV guest kernel with this patch can boot up correctly.

OK, applied for v3.6