Re: [PATCH v12 05/18] xen/mmu/p2m: Refactor the xen_pagetable_init code.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Jan 03, 2014 at 03:47:15PM +0000, Stefano Stabellini wrote:
> On Tue, 31 Dec 2013, Konrad Rzeszutek Wilk wrote:
> > The revector and copying of the P2M only happens when
> > !auto-xlat and on 64-bit builds. It is not obvious from
> > the code, so lets have seperate 32 and 64-bit functions.
> > 
> > We also invert the check for auto-xlat to make the code
> > flow simpler.
> > 
> > Suggested-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > ---
> >  arch/x86/xen/mmu.c | 73 ++++++++++++++++++++++++++++++------------------------
> >  1 file changed, 40 insertions(+), 33 deletions(-)
> > 
> > diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> > index ce563be..d792a69 100644
> > --- a/arch/x86/xen/mmu.c
> > +++ b/arch/x86/xen/mmu.c
> > @@ -1198,44 +1198,40 @@ static void __init xen_cleanhighmap(unsigned long vaddr,
> >  	 * instead of somewhere later and be confusing. */
> >  	xen_mc_flush();
> >  }
> > -#endif
> > -static void __init xen_pagetable_init(void)
> > +static void __init xen_pagetable_p2m_copy(void)
> >  {
> > -#ifdef CONFIG_X86_64
> >  	unsigned long size;
> >  	unsigned long addr;
> > -#endif
> > -	paging_init();
> > -	xen_setup_shared_info();
> > -#ifdef CONFIG_X86_64
> > -	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> > -		unsigned long new_mfn_list;
> > +	unsigned long new_mfn_list;
> > +
> > +	if (xen_feature(XENFEAT_auto_translated_physmap))
> > +		return;
> > +
> > +	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> > +
> > +	/* On 32-bit, we get zero so this never gets executed. */
> 
> Given that this code is already ifdef'ed CONFIG_X86_64, this comment
> should be removed.

Sure.
> 
> 
> > +	new_mfn_list = xen_revector_p2m_tree();
> 
> I take from the comment that new_mfn_list must not be zero. Maybe we
> want a BUG_ON or a WARN_ON?

It can be zero, in which case we don't want to revector.
> 
> 
> > +	if (new_mfn_list && new_mfn_list != xen_start_info->mfn_list) {
> > +		/* using __ka address and sticking INVALID_P2M_ENTRY! */
> > +		memset((void *)xen_start_info->mfn_list, 0xff, size);
> > +
> > +		/* We should be in __ka space. */
> > +		BUG_ON(xen_start_info->mfn_list < __START_KERNEL_map);
> > +		addr = xen_start_info->mfn_list;
> > +		/* We roundup to the PMD, which means that if anybody at this stage is
> > +		 * using the __ka address of xen_start_info or xen_start_info->shared_info
> > +		 * they are in going to crash. Fortunatly we have already revectored
> > +		 * in xen_setup_kernel_pagetable and in xen_setup_shared_info. */
> > +		size = roundup(size, PMD_SIZE);
> > +		xen_cleanhighmap(addr, addr + size);
> >  
> >  		size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> > +		memblock_free(__pa(xen_start_info->mfn_list), size);
> > +		/* And revector! Bye bye old array */
> > +		xen_start_info->mfn_list = new_mfn_list;
> > +	} else
> > +		return;
> 
> This was a normal condition when the function was executed on both
> x86_64 and x86_32. Now that it is only executed on x86_64, is it still
> the case?

It could be. Since this particular patch just moves code I would hesitate
to make changes here. Perhaps a seperate patch after the conditions
under which the xen_revector_p2m_tree() fail can be done?

> 
> 
> > -		/* On 32-bit, we get zero so this never gets executed. */
> > -		new_mfn_list = xen_revector_p2m_tree();
> > -		if (new_mfn_list && new_mfn_list != xen_start_info->mfn_list) {
> > -			/* using __ka address and sticking INVALID_P2M_ENTRY! */
> > -			memset((void *)xen_start_info->mfn_list, 0xff, size);
> > -
> > -			/* We should be in __ka space. */
> > -			BUG_ON(xen_start_info->mfn_list < __START_KERNEL_map);
> > -			addr = xen_start_info->mfn_list;
> > -			/* We roundup to the PMD, which means that if anybody at this stage is
> > -			 * using the __ka address of xen_start_info or xen_start_info->shared_info
> > -			 * they are in going to crash. Fortunatly we have already revectored
> > -			 * in xen_setup_kernel_pagetable and in xen_setup_shared_info. */
> > -			size = roundup(size, PMD_SIZE);
> > -			xen_cleanhighmap(addr, addr + size);
> > -
> > -			size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> > -			memblock_free(__pa(xen_start_info->mfn_list), size);
> > -			/* And revector! Bye bye old array */
> > -			xen_start_info->mfn_list = new_mfn_list;
> > -		} else
> > -			goto skip;
> > -	}
> >  	/* At this stage, cleanup_highmap has already cleaned __ka space
> >  	 * from _brk_limit way up to the max_pfn_mapped (which is the end of
> >  	 * the ramdisk). We continue on, erasing PMD entries that point to page
> > @@ -1255,8 +1251,19 @@ static void __init xen_pagetable_init(void)
> >  	 * anything at this stage. */
> >  	xen_cleanhighmap(MODULES_VADDR, roundup(MODULES_VADDR, PUD_SIZE) - 1);
> >  #endif
> > -skip:
> > +}
> > +#else
> > +static void __init xen_pagetable_p2m_copy(void)
> > +{
> > +	/* Nada! */
> > +}
> >  #endif
> > +
> > +static void __init xen_pagetable_init(void)
> > +{
> > +	paging_init();
> > +	xen_setup_shared_info();
> > +	xen_pagetable_p2m_copy();
> >  	xen_post_allocator_init();
> >  }
> >  static void xen_write_cr2(unsigned long cr2)
> > -- 
> > 1.8.3.1
> >