On 15.07.2024 16:58, Jan Beulich wrote:
> On 15.07.2024 15:58, Oleksii wrote:
>> On Mon, 2024-07-15 at 10:52 +0200, Jan Beulich wrote:
>>> On 12.07.2024 18:22, Oleksii Kurochko wrote:
>>>> + rc = map_pages_to_xen(BOOT_FDT_VIRT_START,
>>>> maddr_to_mfn(base_paddr),
>>>> + SZ_2M >> PAGE_SHIFT,
>>>> + PAGE_HYPERVISOR_RO | _PAGE_BLOCK);
>>>> + if ( rc )
>>>> + panic("Unable to map the device-tree.\n");
>>>> +
>>>> + offset = fdt_paddr % XEN_PT_LEVEL_SIZE(1);
>>>> + fdt_virt = (void *)BOOT_FDT_VIRT_START + offset;
>>>> +
>>>> + if ( fdt_magic(fdt_virt) != FDT_MAGIC )
>>>> + return NULL;
>>>> +
>>>> + size = fdt_totalsize(fdt_virt);
>>>> + if ( size > BOOT_FDT_VIRT_SIZE )
>>>> + return NULL;
>>>> +
>>>> + if ( (offset + size) > SZ_2M )
>>>> + {
>>>> + rc = map_pages_to_xen(BOOT_FDT_VIRT_START + SZ_2M,
>>>> + maddr_to_mfn(base_paddr + SZ_2M),
>>>> + SZ_2M >> PAGE_SHIFT,
>>>> + PAGE_HYPERVISOR_RO | _PAGE_BLOCK);
>>>> + if ( rc )
>>>> + panic("Unable to map the device-tree\n");
>>>> + }
>>>
>>> Why this two part mapping? And why are you mapping perhaps much more
>>> than "size"?
>> I wasn't able to find if RISC-V has a requirement for alignment of FDT
>> address so I decided to follow Arm where FDT is required to be placed
>> on a 8-byte boundary, so FDT can cross a 2MB boundary, so the second
>> 2MB page should be mapped if the FDT is crossing the 2MB boundary.
>
> This explains why you may need to map more than 2Mb (which wasn't the
> question), but it doesn't explain why you need to do it in two steps.
Oh, wait - you know the full size only after having mapped the initial
part. I'm sorry, I didn't spot that early enough.
Jan
