Re: [PATCH v3 9/9] xen/ppc: mm-radix: Allocate all paging structures at runtime

[Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>]

On 3/14/24 5:15 PM, Shawn Anastasio wrote:
> In the initial mm-radix implementation, the in-memory partition and
> process tables required to configure the MMU, as well as the page tables
> themselves were all allocated statically since the boot allocator was
> not yet available.
> 
> Now that it is, allocate these structures at runtime and bump the size
> of the Process Table to its maximum supported value (on POWER9).

After some additional testing, I realized that it is necessary to clear
the memory allocated for these structures before using it, so a small
follow-up is necessary. I will include this with v4 if it is necessary.

diff --git a/xen/arch/ppc/mm-radix.c b/xen/arch/ppc/mm-radix.c
index edae41e0be..f425185259 100644
--- a/xen/arch/ppc/mm-radix.c
+++ b/xen/arch/ppc/mm-radix.c
@@ -37,6 +37,8 @@ static mfn_t __initdata max_alloc_mfn = {0};
  * minimum mfns that have been allocated. This information is used by
  * setup_initial_mapping to include the allocated pages in the initial
  * page mapping.
+ *
+ * Additionally, allocated pages are zeroed before return.
  */
 static mfn_t __init initial_page_alloc(unsigned long nr_pfns,
                                        unsigned long pfn_align)
@@ -49,6 +51,8 @@ static mfn_t __init initial_page_alloc(unsigned long
nr_pfns,
     min_alloc_mfn = _mfn(min(mfn_x(min_alloc_mfn), mfn_x(mfn_first)));
     max_alloc_mfn = _mfn(max(mfn_x(max_alloc_mfn), mfn_x(mfn_last)));

+    memset(__va(mfn_to_maddr(mfn_first)), 0, nr_pfns << PAGE_SHIFT);
+
     return mfn_first;
 }