> On 23 Feb 2023, at 15:09, Bertrand Marquis <[email protected]> wrote:
>
> Hi Julien,
>
>> On 27 Jan 2023, at 20:55, Julien Grall <[email protected]> wrote:
>>
>> From: Julien Grall <[email protected]>
>>
>> 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. 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 <[email protected]>
>> Tested-by: Luca Fancellu <[email protected]>
>> Reviewed-by: Michal Orzel <[email protected]>
>
> With the finding for the comparison to 4 and not 2 found by Michal fixed:
> Reviewed-by: Bertrand Marquis <[email protected]
> <mailto:[email protected]>>
Sorry for that:
Reviewed-by: Bertrand Marquis <[email protected]>
Cheers
Bertrand
>
> Cheers
> Bertrand
>
>>
>> ---
>> 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 | 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 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..e388462c23d1 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]
>> + * (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
>> *
>> * 32G - 64G Frametable: 56 bytes per page for 2TB of RAM
>> *
>> - * 0x0000008000000000 - 0x00007fffffffffff (127.5TB, L0 slots [1..255])
>> + * 0x0000028000000000 - 0x00007fffffffffff (125TB, L0 slots [5..255])
>> * Unused
>> *
>> * 0x0000800000000000 - 0x000084ffffffffff (5TB, L0 slots [256..265])
>> @@ -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(4) + _AT(vaddr_t, MB(2)))
>> +#endif
>> +
>> #define XEN_VIRT_SIZE _AT(vaddr_t, MB(2))
>>
>> #define FIXMAP_VIRT_START (XEN_VIRT_START + XEN_VIRT_SIZE)
>> @@ -163,10 +179,6 @@
>>
>> #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 f758cad545fa..0b0edf28d57a 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
>> @@ -496,10 +496,11 @@ 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
