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

From: Juergen Gross
Date: Wed Feb 18 2015 - 05:43:04 EST

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 =
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++;
__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().

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