Hi Stefano,
On 11/06/2019 23:35, Stefano Stabellini wrote:
On Tue, 14 May 2019, Julien Grall wrote:
At the moment, the flags are not enough to describe what kind of update
will done on the VA range. They need to be used in conjunction with the
enum xenmap_operation.
It would be more convenient to have all the information for the update
in a single place.
Two new flags are added to remove the relience on xenmap_operation:
- _PAGE_PRESENT: Indicate whether we are adding/removing the mapping
- _PAGE_POPULATE: Indicate whether we only populate page-tables
Signed-off-by: Julien Grall <julien.gr...@arm.com>
Reviewed-by: Andrii Anisov <andrii_ani...@epam.com>
Looking ahead in this series, I know that this is done so that later on
you can remove enum xenmap_operation. But what is the end goal? Why do
we want to remove enum xenmap_operation? I guess it is to make the code
more reusable?
The end goal is to streamline as much as possible to page-table update. I wanted
to have all the information in flags because it is much easier to reason with
one variable over two variables.
Furthermore, x86 code allows map_pages_to_xen(...) to destroy mappings but not
the underlying page-tables. This is used for instance for the vunmap to avoid
re-creating the page-tables afterwards. I have been thinking to introduce
similar things on Arm.
Keeping the xenmap_operation would make it awkward to support it because you
would have to translate the flags to the actual operations.
---
Changes in v2:
- Add Andrii's reviewed-by
---
xen/arch/arm/mm.c | 2 +-
xen/include/asm-arm/page.h | 9 +++++++--
2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 9de2a1150f..2192dede55 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1083,7 +1083,7 @@ int map_pages_to_xen(unsigned long virt,
int populate_pt_range(unsigned long virt, unsigned long nr_mfns)
{
- return xen_pt_update(RESERVE, virt, INVALID_MFN, nr_mfns, 0);
+ return xen_pt_update(RESERVE, virt, INVALID_MFN, nr_mfns, _PAGE_POPULATE);
}
int destroy_xen_mappings(unsigned long v, unsigned long e)
diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 2bcdb0f1a5..caf2fac1ff 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -76,6 +76,8 @@
*
* [0:2] Memory Attribute Index
* [3:4] Permission flags
+ * [5] Present bit
+ * [6] Populate page table
[5] is pretty clear. As a nit, I would probably write:
[5] Page Present
Better alternative, I will update the comment.
because there is no need to say "bit", the [5] means it is a bit.
Otherwise, something like the following:
[5] Present in memory
but it's unimportant.
It's [6] that we might want to explain a bit better: if we say "Populate
page table" then every time we want the Xen pagetable to be populated we
would need to pass _PAGE_POPULATE, even when the page is present in
memory. Do you see what I mean? I am not entirely sure how to make it
clearer. Maybe:
To be honest, I was not entirely happy with the current comment. But I also
wasn't able to find a better one :).
[6] Only populate page tables
I am happy with this alternative. I will update the comment.
Cheers,
--
Julien Grall
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