[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] xen/arm: mm: optimize setup_pagetables



Hi Peng,

I would rename the title: "xen/arm: mm: remove unnecessary tlb flush in setup_pagetables".

On 11/05/2016 08:59, Peng Fan wrote:
Before relocating xen to high address, need to build
the mapping BOOT_RELOC_VIRT_START to xen_paddr into
boot_pgtable and xen_pgtable.

In setup_pagetables, relocate_xen will switch the root
page table from boot_pgtable to xen_pgtable/cpu0_pgtable.

Before relocate_xen:
If touching xen_pgtable, no need to flush_xen_data_tlb_range_va_local.
We only need to flush tlb when touch boot_pgtable.
And no need to use write_pte for xen_pgtable, we can simply use
"xen_second[second_table_offset(dest_va)] = pte;"

Also move the piece code near DTB/Fixmap/XEN_VIRT_START to
be more easier to understand.

The commit message is rather hard to understand. Can you please rework it say: - CPU0 is using the boot pages table and xen_second is not part of them => No need to flush the TLB
  - Clean up the code (i.e the code movement)

However, I would prefer to see 2 patches, one for removing the tlb flush, the other to move the code.

[...]

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 94ea054..bebd82f 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -443,12 +443,6 @@ void __init setup_pagetables(unsigned long 
boot_phys_offset, paddr_t xen_paddr)
      lpae_t pte, *p;
      int i;

-    /* Map the destination in the boot misc area. */
-    dest_va = BOOT_RELOC_VIRT_START;
-    pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT, WRITEALLOC);
-    write_pte(xen_second + second_table_offset(dest_va), pte);
-    flush_xen_data_tlb_range_va_local(dest_va, SECOND_SIZE);
-
      /* Calculate virt-to-phys offset for the new location */
      phys_offset = xen_paddr - (unsigned long) _start;

@@ -498,6 +492,11 @@ void __init setup_pagetables(unsigned long 
boot_phys_offset, paddr_t xen_paddr)
      /* Map the destination in the boot misc area. */
      dest_va = BOOT_RELOC_VIRT_START;
      pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT, WRITEALLOC);
+    xen_second[second_table_offset(dest_va)] = pte;
+
+    /* Map the destination in the boot misc area. */
+    dest_va = BOOT_RELOC_VIRT_START;
+    pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT, WRITEALLOC);

Why do you need to recompute "pte" and "dest_va"? They will be the same for "boot_second" and "xen_second".

Also, I think the code is still confusing in the current state because of the comments "Map the destination in the boot misc area.". They need to be updated to differentiate xen_second vs boot_second.

      write_pte(boot_second + second_table_offset(dest_va), pte);
      flush_xen_data_tlb_range_va_local(dest_va, SECOND_SIZE);
  #ifdef CONFIG_ARM_64


Regards,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.