Hi Michal,
On 17/04/2023 08:28, Michal Orzel wrote:
On 16/04/2023 16:32, Julien Grall wrote:
From: Julien Grall <jgr...@amazon.com>
Xen is currently not fully compliant with the Arm Arm because it will
switch the TTBR with the MMU on.
In order to be compliant, we need to disable the MMU before
switching the TTBR. The implication is the page-tables should
contain an identity mapping of the code switching the TTBR.
In most of the case we expect Xen to be loaded in low memory. I am aware
of one platform (i.e AMD Seattle) where the memory start above 512GB.
To give us some slack, consider that Xen may be loaded in the first 2TB
of the physical address space.
The memory layout is reshuffled to keep the first four slots of the zeroeth
level free. All the regions currently in L0 slot 0 will not be part of
slot 4 (2TB). This requires a slight tweak of the boot code because
XEN_VIRT_START (2TB + 2MB) cannot be used as an immediate.
This reshuffle will make trivial to create a 1:1 mapping when Xen is
loaded below 2TB.
Lastly, take the opportunity to check a compile time if any of the
s/a/at/ compile time
regions may overlap with the reserved area for identity mapping.
Signed-off-by: Julien Grall <jgr...@amazon.com>
----
Changes in v7:
- Remove all tags
- Add BUILD_BUG_ON()s
- Don't forget to update FRAMETABLE_VIRT_START and
VMAP_VIRT_START
Changes in v6:
- Correct the BUILD_BUG_ON(), Xen virtual address should be
above 2TB (i.e. slot0 > 4).
- Add Bertrand's reviewed-by
Changes in v5:
- We are reserving 4 slots rather than 2.
- Fix the addresses in the layout comment.
- Fix the size of the region in the layout comment
- Add Luca's tested-by (the reviewed-by was not added
because of the changes requested by Michal)
- Add Michal's reviewed-by
Changes in v4:
- Correct the documentation
- The start address is 2TB, so slot0 is 4 not 2.
Changes in v2:
- Reword the commit message
- Load Xen at 2TB + 2MB
- Update the documentation to reflect the new layout
---
xen/arch/arm/arm64/head.S | 3 ++-
xen/arch/arm/include/asm/config.h | 38 +++++++++++++++++++++----------
xen/arch/arm/mm.c | 23 +++++++++++++++----
3 files changed, 46 insertions(+), 18 deletions(-)
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 4a3f87117c83..663f5813b12e 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -607,7 +607,8 @@ create_page_tables:
* need an additional 1:1 mapping, the virtual mapping will
* suffice.
*/
- cmp x19, #XEN_VIRT_START
+ ldr x0, =XEN_VIRT_START
+ cmp x19, x0
bne 1f
ret
1:
diff --git a/xen/arch/arm/include/asm/config.h
b/xen/arch/arm/include/asm/config.h
index 5df0e4c4959b..2cfe5e480256 100644
--- a/xen/arch/arm/include/asm/config.h
+++ b/xen/arch/arm/include/asm/config.h
@@ -72,16 +72,13 @@
#include <xen/page-size.h>
/*
- * Common ARM32 and ARM64 layout:
+ * ARM32 layout:
* 0 - 2M Unmapped
* 2M - 4M Xen text, data, bss
* 4M - 6M Fixmap: special-purpose 4K mapping slots
* 6M - 10M Early boot mapping of FDT
* 10M - 12M Livepatch vmap (if compiled in)
*
- * ARM32 layout:
- * 0 - 12M <COMMON>
- *
* 32M - 128M Frametable: 32 bytes per page for 12GB of RAM
* 256M - 1G VMAP: ioremap and early_ioremap use this virtual address
* space
@@ -90,14 +87,23 @@
* 2G - 4G Domheap: on-demand-mapped
*
* ARM64 layout:
- * 0x0000000000000000 - 0x0000007fffffffff (512GB, L0 slot [0])
- * 0 - 12M <COMMON>
+ * 0x0000000000000000 - 0x000001ffffffffff (2TB, L0 slots [0..3])
+ *
+ * Reserved to identity map Xen
+ *
+ * 0x0000020000000000 - 0x0000027fffffffff (512GB, L0 slot [4]
missing closing parenthesis at the end of line
This can be done on commit, so:
Thanks for spotting the typoes. I will update on commit.
Reviewed-by: Michal Orzel <michal.or...@amd.com>
Cheers,
--
Julien Grall
