Re: [PATCH 1/2] mm, Make __get_user_pages return -EHWPOISON for HWPOISON page

[Huang Ying <ying.huang@intel.com>]

On Wed, 2010-04-28 at 05:47 +0800, Andrew Morton wrote:
> On Tue, 27 Apr 2010 15:04:18 +0800
> Huang Ying <ying.huang@intel.com> wrote:
> 
> > With this patch, the caller of __get_user_pages can distinguish
> > HWPOISON page from general FAULT page. This is needed by KVM, where
> > UCR MCE should be relayed to guest for HWPOISON page, while
> > instruction emulation and MMIO will be tried for general FAULT page.
> > 
> > Signed-off-by: Huang Ying <ying.huang@intel.com>
> > ---
> >  include/asm-generic/errno.h |    2 ++
> >  mm/memory.c                 |    5 +++--
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> > 
> > --- a/include/asm-generic/errno.h
> > +++ b/include/asm-generic/errno.h
> > @@ -108,4 +108,6 @@
> >  
> >  #define ERFKILL		132	/* Operation not possible due to RF-kill */
> >  
> > +#define EHWPOISON	133	/* Memory page has hardware error */
> > +
> >  #endif
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -1432,9 +1432,10 @@ int __get_user_pages(struct task_struct
> >  				if (ret & VM_FAULT_ERROR) {
> >  					if (ret & VM_FAULT_OOM)
> >  						return i ? i : -ENOMEM;
> > -					if (ret &
> > -					    (VM_FAULT_HWPOISON|VM_FAULT_SIGBUS))
> > +					if (ret & VM_FAULT_SIGBUS)
> >  						return i ? i : -EFAULT;
> > +					if (ret & VM_FAULT_HWPOISON)
> > +						return i ? i : -EHWPOISON;
> >  					BUG();
> >  				}
> >  				if (ret & VM_FAULT_MAJOR)
> > 
> 
> This will cause various code paths (eg: fs/direct-io.c) to return
> -EHWPOISON to userspace, will it not?

Yes. I think it may be returned to userspace. Do we need to keep the
userspace errno interface like this?

If it is, we can check whether the virtual page is hwpoisoned via going
through the page table because the hwpoisoned virtual page has a special
swap entry in page table.

Best Regards,
Huang Ying