Re: [Xen-devel] [PATCH 02/11] xen/x86: Use memblock_reserve for sensitive areas.

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

On Fri, Aug 17, 2012 at 06:35:12PM +0100, Stefano Stabellini wrote:
> On Thu, 16 Aug 2012, Konrad Rzeszutek Wilk wrote:
> > instead of a big memblock_reserve. This way we can be more
> > selective in freeing regions (and it also makes it easier
> > to understand where is what).
> > 
> > [v1: Move the auto_translate_physmap to proper line]
> > [v2: Per Stefano suggestion add more comments]
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> 
> much better now!

Thought interestingly enough it breaks 32-bit dom0s (and only dom0s).
Will have a revised patch posted shortly.

> 
> >  arch/x86/xen/enlighten.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/xen/p2m.c       |    5 ++++
> >  arch/x86/xen/setup.c     |    9 --------
> >  3 files changed, 53 insertions(+), 9 deletions(-)
> > 
> > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > index ff962d4..e532eb5 100644
> > --- a/arch/x86/xen/enlighten.c
> > +++ b/arch/x86/xen/enlighten.c
> > @@ -998,7 +998,54 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
> >  
> >  	return ret;
> >  }
> > +/*
> > + * If the MFN is not in the m2p (provided to us by the hypervisor) this
> > + * function won't do anything. In practice this means that the XenBus
> > + * MFN won't be available for the initial domain. */
> > +static void __init xen_reserve_mfn(unsigned long mfn)
> > +{
> > +	unsigned long pfn;
> > +
> > +	if (!mfn)
> > +		return;
> > +	pfn = mfn_to_pfn(mfn);
> > +	if (phys_to_machine_mapping_valid(pfn))
> > +		memblock_reserve(PFN_PHYS(pfn), PAGE_SIZE);
> > +}
> > +static void __init xen_reserve_internals(void)
> > +{
> > +	unsigned long size;
> > +
> > +	if (!xen_pv_domain())
> > +		return;
> > +
> > +	/* xen_start_info does not exist in the M2P, hence can't use
> > +	 * xen_reserve_mfn. */
> > +	memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
> > +
> > +	xen_reserve_mfn(PFN_DOWN(xen_start_info->shared_info));
> > +	xen_reserve_mfn(xen_start_info->store_mfn);
> >  
> > +	if (!xen_initial_domain())
> > +		xen_reserve_mfn(xen_start_info->console.domU.mfn);
> > +
> > +	if (xen_feature(XENFEAT_auto_translated_physmap))
> > +		return;
> > +
> > +	/*
> > +	 * ALIGN up to compensate for the p2m_page pointing to an array that
> > +	 * can partially filled (look in xen_build_dynamic_phys_to_machine).
> > +	 */
> > +
> > +	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> > +
> > +	/* We could use xen_reserve_mfn here, but would end up looping quite
> > +	 * a lot (and call memblock_reserve for each PAGE), so lets just use
> > +	 * the easy way and reserve it wholesale. */
> > +	memblock_reserve(__pa(xen_start_info->mfn_list), size);
> > +
> > +	/* The pagetables are reserved in mmu.c */
> > +}
> >  void xen_setup_shared_info(void)
> >  {
> >  	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> > @@ -1362,6 +1409,7 @@ asmlinkage void __init xen_start_kernel(void)
> >  	xen_raw_console_write("mapping kernel into physical memory\n");
> >  	pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);
> >  
> > +	xen_reserve_internals();
> >  	/* Allocate and initialize top and mid mfn levels for p2m structure */
> >  	xen_build_mfn_list_list();
> >  
> > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> > index e4adbfb..6a2bfa4 100644
> > --- a/arch/x86/xen/p2m.c
> > +++ b/arch/x86/xen/p2m.c
> > @@ -388,6 +388,11 @@ void __init xen_build_dynamic_phys_to_machine(void)
> >  	}
> >  
> >  	m2p_override_init();
> > +
> > +	/* NOTE: We cannot call memblock_reserve here for the mfn_list as there
> > +	 * isn't enough pieces to make it work (for one - we are still using the
> > +	 * Xen provided pagetable). Do it later in xen_reserve_internals.
> > +	 */
> >  }
> >  
> >  unsigned long get_phys_to_machine(unsigned long pfn)
> > diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> > index a4790bf..9efca75 100644
> > --- a/arch/x86/xen/setup.c
> > +++ b/arch/x86/xen/setup.c
> > @@ -424,15 +424,6 @@ char * __init xen_memory_setup(void)
> >  	e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
> >  			E820_RESERVED);
> >  
> > -	/*
> > -	 * Reserve Xen bits:
> > -	 *  - mfn_list
> > -	 *  - xen_start_info
> > -	 * See comment above "struct start_info" in <xen/interface/xen.h>
> > -	 */
> > -	memblock_reserve(__pa(xen_start_info->mfn_list),
> > -			 xen_start_info->pt_base - xen_start_info->mfn_list);
> > -
> >  	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
> >  
> >  	return "Xen";
> > -- 
> > 1.7.7.6
> > 
> > 
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