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Date: Fri, 3 Jan 2014 11:02:00 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
mukesh.rathor@...cle.com
Subject: Re: [PATCH v12 05/18] xen/mmu/p2m: Refactor the xen_pagetable_init
code.
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@...citrix.com>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.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
> >
--
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