Re: [Xen-devel] [PATCH 02/13] xen: anchor linear p2m list in shared info structure

[Juergen Gross]

On 02/18/2015 11:32 AM, David Vrabel wrote:
> On 18/02/15 06:51, Juergen Gross wrote:
> > The linear p2m list should be anchored in the shared info structure
>
> I'm not really sure what you mean by "anchored".

Bad wording? What about:

The virtual address of the linear p2m list should be stored in the
shared info structure.

> > read by the Xen tools to be able to support 64 bit pv-domains larger
> > than 512 MB. Additionally the linear p2m list interface includes a
> > generation count which is changed prior to and after each mapping
> > change of the p2m list. Reading the generation count the Xen tools can
> > detect changes of the mappings and re-read the p2m list eventually.
> [...]
> > --- a/arch/x86/xen/p2m.c
> > +++ b/arch/x86/xen/p2m.c
> > @@ -256,6 +256,10 @@ void xen_setup_mfn_list_list(void)
> >   	HYPERVISOR_shared_info->arch.pfn_to_mfn_frame_list_list =
> >   		virt_to_mfn(p2m_top_mfn);
> >   	HYPERVISOR_shared_info->arch.max_pfn = xen_max_p2m_pfn;
> > +	HYPERVISOR_shared_info->arch.p2m_generation = 0;
> > +	HYPERVISOR_shared_info->arch.p2m_vaddr = (unsigned long)xen_p2m_addr;
> > +	HYPERVISOR_shared_info->arch.p2m_cr3 =
> > +		xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));
> >   }
> >
> >   /* Set up p2m_top to point to the domain-builder provided p2m pages */
> > @@ -469,8 +473,10 @@ static pte_t *alloc_p2m_pmd(unsigned long addr, pte_t *pte_pg)
> >
> >   		ptechk = lookup_address(vaddr, &level);
> >   		if (ptechk == pte_pg) {
> > +			HYPERVISOR_shared_info->arch.p2m_generation++;
> >   			set_pmd(pmdp,
> >   				__pmd(__pa(pte_newpg[i]) | _KERNPG_TABLE));
> > +			HYPERVISOR_shared_info->arch.p2m_generation++;
>
> Do these increments of p2m_generation need to be atomic?

Hmm, they are done under lock. I don't think the compiler is allowed to
reorder the writes to p2m_generation across set_pmd().


Juergen
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/