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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4 8/8] xen/arm32: head: Use a page mapping for the 1:1 mapping in create_page_tables()
On Tue, 17 Sep 2019, Julien Grall wrote:
> At the moment the function create_page_tables() will use 1GB/2MB
> mapping for the identity mapping. As we don't know what is present
> before and after Xen in memory, we may end up to map
> device/reserved-memory with cacheable memory. This may result to
> mismatched attributes as other users may access the same region
> differently.
>
> To prevent any issues, we should only map the strict minimum in the
> 1:1 mapping. A check in xen.lds.S already guarantees anything
> necessary for turning on the MMU fits in a page (at the moment 4K).
>
> As only one page will be mapped for the 1:1 mapping, it is necessary
> to pre-allocate a page for the 3rd level table.
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>
> ---
> Changes in v4:
> - Use XEN_{FIRST, SECOND}_SLOT rather than hardcoded value
> - Don't pre-link the page-tables for the 1:1 mapping
>
> Changes in v3:
> - Patch added
> ---
> xen/arch/arm/arm32/head.S | 121
> +++++++++++++++++++---------------------------
> xen/arch/arm/mm.c | 2 +-
> 2 files changed, 50 insertions(+), 73 deletions(-)
>
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 175f0c9760..7b5109db26 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -447,73 +447,13 @@ ENDPROC(cpu_init)
> * r6 : Identity map in place
> */
> create_page_tables:
> - /*
> - * If Xen is loaded at exactly XEN_VIRT_START then we don't
> - * need an additional 1:1 mapping, the virtual mapping will
> - * suffice.
> - */
> - cmp r9, #XEN_VIRT_START
> - moveq r6, #1 /* r6 := identity map now in place */
> - movne r6, #0 /* r6 := identity map not yet in place
> */
> -
> - ldr r4, =boot_pgtable
> - add r4, r4, r10 /* r4 := paddr (boot_pagetable) */
> -
> - /* Setup boot_pgtable: */
> - ldr r1, =boot_second
> - add r1, r1, r10 /* r1 := paddr (boot_second) */
> -
> - /* ... map boot_second in boot_pgtable[0] */
> - orr r2, r1, #PT_UPPER(PT) /* r2:r3 := table map of boot_second */
> - orr r2, r2, #PT_LOWER(PT) /* (+ rights for linear PT) */
> - mov r3, #0x0
> - strd r2, r3, [r4, #0] /* Map it in slot 0 */
> -
> - /* ... map of paddr(start) in boot_pgtable */
> - lsrs r1, r9, #FIRST_SHIFT /* Offset of base paddr in boot_pgtable
> */
> - beq 1f /* If it is in slot 0 then map in
> boot_second
> - * later on */
> - lsl r2, r1, #FIRST_SHIFT /* Base address for 1GB mapping */
> - orr r2, r2, #PT_UPPER(MEM) /* r2:r3 := section map */
> - orr r2, r2, #PT_LOWER(MEM)
> - lsl r1, r1, #3 /* r1 := Slot offset */
> - mov r3, #0x0
> - strd r2, r3, [r4, r1] /* Mapping of paddr(start) */
> - mov r6, #1 /* r6 := identity map now in place */
> -
> -1: /* Setup boot_second: */
> - ldr r4, =boot_second
> - add r4, r4, r10 /* r4 := paddr (boot_second) */
> -
> - ldr r1, =boot_third
> - add r1, r1, r10 /* r1 := paddr (boot_third) */
> -
> - /* ... map boot_third in boot_second[1] */
> - orr r2, r1, #PT_UPPER(PT) /* r2:r3 := table map of boot_third */
> - orr r2, r2, #PT_LOWER(PT) /* (+ rights for linear PT) */
> - mov r3, #0x0
> - strd r2, r3, [r4, #8] /* Map it in slot 1 */
> -
> - /* ... map of paddr(start) in boot_second */
> - cmp r6, #1 /* r6 is set if already created */
> - beq 1f
> - lsr r2, r9, #SECOND_SHIFT /* Offset of base paddr in boot_second
> */
> - ldr r3, =LPAE_ENTRY_MASK
> - and r1, r2, r3
> - cmp r1, #1
> - beq virtphys_clash /* It's in slot 1, which we cannot
> handle */
> -
> - lsl r2, r2, #SECOND_SHIFT /* Base address for 2MB mapping */
> - orr r2, r2, #PT_UPPER(MEM) /* r2:r3 := section map */
> - orr r2, r2, #PT_LOWER(MEM)
> - mov r3, #0x0
> - lsl r1, r1, #3 /* r1 := Slot offset */
> - strd r2, r3, [r4, r1] /* Mapping of paddr(start) */
> - mov r6, #1 /* r6 := identity map now in place */
> + /* Prepare the page-tables for mapping Xen */
> + ldr r0, =XEN_VIRT_START
> + create_table_entry boot_pgtable, boot_second, r0, FIRST_SHIFT
> + create_table_entry boot_second, boot_third, r0, SECOND_SHIFT
>
> /* Setup boot_third: */
> -1: ldr r4, =boot_third
> - add r4, r4, r10 /* r4 := paddr (boot_third) */
> + adr_l r4, boot_third, mmu=0
>
> lsr r2, r9, #THIRD_SHIFT /* Base address for 4K mapping */
> lsl r2, r2, #THIRD_SHIFT
> @@ -530,16 +470,53 @@ create_page_tables:
> blo 1b
>
> /*
> - * Defer fixmap and dtb mapping until after paging enabled, to
> - * avoid them clashing with the 1:1 mapping.
> + * If Xen is loaded at exactly XEN_VIRT_START then we don't
> + * need an additional 1:1 mapping, the virtual mapping will
> + * suffice.
> */
> + cmp r9, #XEN_VIRT_START
> + moveq pc, lr
>
> - /* boot pagetable setup complete */
> +1:
As far as I can tell, this 1 label is unused. If so, we should remove
it. With that gone:
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> + /*
> + * Setup the 1:1 mapping so we can turn the MMU on. Note that
> + * only the first page of Xen will be part of the 1:1 mapping.
> + */
> +
> + /*
> + * Find the first slot used. If the slot is not XEN_FIRST_SLOT,
> + * then the 1:1 mapping will use its own set of page-tables from
> + * the second level.
> + */
> + lsr r1, r9, #FIRST_SHIFT
> + mov_w r0, LPAE_ENTRY_MASK
> + and r1, r1, r0 /* r1 := first slot */
> + cmp r1, #XEN_FIRST_SLOT
> + beq 1f
> + create_table_entry boot_pgtable, boot_second_id, r9, FIRST_SHIFT
> + b link_from_second_id
> +
> +1:
> + /*
> + * Find the second slot used. If the slot is XEN_SECOND_SLOT, then
> the
> + * 1:1 mapping will use its own set of page-tables from the
> + * third level. For slot XEN_SECOND_SLOT, Xen is not yet able to
> handle
> + * it.
> + */
> + lsr r1, r9, #SECOND_SHIFT
> + mov_w r0, LPAE_ENTRY_MASK
> + and r1, r1, r0 /* r1 := second slot */
> + cmp r1, #XEN_SECOND_SLOT
> + beq virtphys_clash
> + create_table_entry boot_second, boot_third_id, r9, SECOND_SHIFT
> + b link_from_third_id
> +
> +link_from_second_id:
> + create_table_entry boot_second_id, boot_third_id, r9, SECOND_SHIFT
> +link_from_third_id:
> + create_mapping_entry boot_third_id, r9, r9
> + mov pc, lr
>
> - cmp r6, #1 /* Did we manage to create an identity
> mapping ? */
> - moveq pc, lr
> - PRINT("Unable to build boot page tables - Failed to identity map
> Xen.\r\n")
> - b fail
> virtphys_clash:
> /* Identity map clashes with boot_third, which we cannot handle yet
> */
> PRINT("- Unable to build boot page tables - virt and phys addresses
> clash. -\r\n")
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 72ffea7472..9e0fdc39f9 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -105,9 +105,9 @@ DEFINE_BOOT_PAGE_TABLE(boot_pgtable);
> #ifdef CONFIG_ARM_64
> DEFINE_BOOT_PAGE_TABLE(boot_first);
> DEFINE_BOOT_PAGE_TABLE(boot_first_id);
> +#endif
> DEFINE_BOOT_PAGE_TABLE(boot_second_id);
> DEFINE_BOOT_PAGE_TABLE(boot_third_id);
> -#endif
> DEFINE_BOOT_PAGE_TABLE(boot_second);
> DEFINE_BOOT_PAGE_TABLE(boot_third);
>
> --
> 2.11.0
>
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