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Re: [PATCH v3 12/18] xen/arm64: Rework the memory layout
Hi Stefano,
On 13/12/2022 01:22, Stefano Stabellini wrote:
On Mon, 12 Dec 2022, Julien Grall wrote:
From: Julien Grall <jgrall@xxxxxxxxxx>
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 two slots of the zeroeth
level free. Xen will now be loaded at (2TB + 2MB). This requires a slight
tweak of the boot code because XEN_VIRT_START cannot be used as an
immediate.
This reshuffle will make trivial to create a 1:1 mapping when Xen is
loaded below 2TB.
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
---
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 | 34 +++++++++++++++++++++----------
xen/arch/arm/mm.c | 11 +++++-----
3 files changed, 31 insertions(+), 17 deletions(-)
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index ad014716db6f..23c2c7491db2 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 6c1b762e976d..9fe6bfeeeb95 100644
--- a/xen/arch/arm/include/asm/config.h
+++ b/xen/arch/arm/include/asm/config.h
@@ -72,15 +72,12 @@
#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>
+ * 10M - 12M Livepatch vmap (if compiled in)
*
* 32M - 128M Frametable: 24 bytes per page for 16GB of RAM
* 256M - 1G VMAP: ioremap and early_ioremap use this virtual address
@@ -90,8 +87,17 @@
* 2G - 4G Domheap: on-demand-mapped
*
* ARM64 layout:
- * 0x0000000000000000 - 0x0000007fffffffff (512GB, L0 slot [0])
- * 0 - 12M <COMMON>
+ * 0x0000000000000000 - 0x00001fffffffffff (2TB, L0 slots [0..1])
+ *
Extra blank line
I have removed it.
+ * Reserved to identity map Xen
+ *
+ * 0x0000020000000000 - 0x000028fffffffff (512TB, L0 slot [2]
+ * (Relative offsets)
+ * 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)
*
* 1G - 2G VMAP: ioremap and early_ioremap
*
@@ -107,7 +113,17 @@
* Unused
*/
+#ifdef CONFIG_ARM_32
#define XEN_VIRT_START _AT(vaddr_t, MB(2))
+#else
+
+#define SLOT0_ENTRY_BITS 39
+#define SLOT0(slot) (_AT(vaddr_t,slot) << SLOT0_ENTRY_BITS)
+#define SLOT0_ENTRY_SIZE SLOT0(1)
+
+#define XEN_VIRT_START (SLOT0(2) + _AT(vaddr_t, MB(2)))
+#endif
Sorry for the silly question and I apologize if I got the math wrong.
1<<39 is 512MB, so:
Looking at how you use below, I am guessing you mean GB rather than MB.
slot0 is [0..512MB]
slot1 is [512MB..1TB]
slot2 is [1TB..1.5TB]
slot3 is [1.5TB..2TB]
slot4 is [2TB..2.5TB]
So, if we want Xen just above 2TB we should use slot4? Which would be
SLOT0(4) ?
You are right. I will update the code.
#define XEN_VIRT_SIZE _AT(vaddr_t, MB(2))
#define FIXMAP_VIRT_START (XEN_VIRT_START + XEN_VIRT_SIZE)
@@ -164,10 +180,6 @@
#else /* ARM_64 */
-#define SLOT0_ENTRY_BITS 39
-#define SLOT0(slot) (_AT(vaddr_t,slot) << SLOT0_ENTRY_BITS)
-#define SLOT0_ENTRY_SIZE SLOT0(1)
-
#define VMAP_VIRT_START GB(1)
#define VMAP_VIRT_SIZE GB(1)
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index d0b1cf55f550..cc11f5c639e6 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -153,7 +153,7 @@ static void __init __maybe_unused build_assertions(void)
#endif
/* Page table structure constraints */
#ifdef CONFIG_ARM_64
- BUILD_BUG_ON(zeroeth_table_offset(XEN_VIRT_START));
+ BUILD_BUG_ON(zeroeth_table_offset(XEN_VIRT_START) < 2);
#endif
BUILD_BUG_ON(first_table_offset(XEN_VIRT_START));
#ifdef CONFIG_ARCH_MAP_DOMAIN_PAGE
@@ -498,10 +498,11 @@ void __init setup_pagetables(unsigned long
boot_phys_offset)
phys_offset = boot_phys_offset;
#ifdef CONFIG_ARM_64
- p = (void *) xen_pgtable;
- p[0] = pte_of_xenaddr((uintptr_t)xen_first);
- p[0].pt.table = 1;
- p[0].pt.xn = 0;
+ pte = pte_of_xenaddr((uintptr_t)xen_first);
+ pte.pt.table = 1;
+ pte.pt.xn = 0;
+ xen_pgtable[zeroeth_table_offset(XEN_VIRT_START)] = pte;
+
p = (void *) xen_first;
#else
p = (void *) cpu0_pgtable;
--
2.38.1
Cheers,
--
Julien Grall
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