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Michal Orzel
6d317b10f8
At the moment, Xen does not support booting gzip compressed uImages.
This is because we are trying to decompress the kernel before probing
the u-boot header. This leads to a failure as the header always appears
at the top of the image (and therefore obscuring the gzip header).
Move the call to kernel_uimage_probe before kernel_decompress and make
the function self-containing by taking the following actions:
- take a pointer to struct bootmodule as a parameter,
- check the comp field of a u-boot header to determine compression type,
- in case of compressed image, call kernel_decompress passing uImage
header size as an offset to gzip header,
- set up zimage.{kernel_addr,len} accordingly,
- return -ENOENT in case of a u-boot header not found to distinguish it
amongst other return values and make it the only case for falling
through to try to probe other image types.
Modify kernel_decompress to take an additional parameter being an offset
to a gzip header from start address. This is needed so that a function
can first operate on a region containing actually compressed kernel (in case
of compressed uImage, size of u-boot header is an offset to a gzip header)
and then at the end pass the entire region (as it was before taking an offset
into account) to fw_unreserved_regions for freeing.
This approach avoids splitting the uImage probing into 2 stages (executed
before and after decompression) which otherwise would be necessary to
properly parse header, update boot module start and size before
decompression and update zimage.{kernel_addr,len} afterwards.
Remove the limitation from the booting.txt documentation.
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewwed-by: Julien Grall <jgrall@amazon.com>
73 lines
2.7 KiB
Plaintext
73 lines
2.7 KiB
Plaintext
Booting Xen
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===========
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Xen follows the zImage protocol defined for 32-bit ARM Linux[1] and the
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Image protocol defined for ARM64 Linux[2].
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In both cases the recommendation to boot in HYP/EL2 mode is a strict
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requirement for Xen.
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The exceptions to this on 32-bit ARM are as follows:
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Xen does not require the machine type to be passed in r1. This
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register is ignored (so may be invalid or the actual machine type).
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Xen does not support the ATAG list and requires Device
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Tree. Therefore r2 must point to the physical address of device tree
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block (dtb) in system RAM.
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NOTE: although Xen uses the zImage protocol there is no compression
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actually used. This should be transparent to the bootloader. The
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zImage protocol should still be used and not the stricter "raw
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(non-zImage)" protocol described in arm/Booting.
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There are no exception on 64-bit ARM.
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Booting Guests
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--------------
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Xen supports the legacy image header[3], zImage protocol for 32-bit
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ARM Linux[1] and Image protocol defined for ARM64[2].
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Until Xen 4.17, in case of legacy image protocol, Xen ignored the load
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address and entry point specified in the header. This has now changed.
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Now, it loads the image at the load address provided in the header.
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And the entry point is used as the kernel start address.
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A deviation from uboot is that, Xen treats "load address == 0x0" as
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position independent execution (PIE). Thus, Xen will load such an image
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at an address it considers appropriate. Also, user cannot specify the
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entry point of a PIE image since the start address cennot be
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predetermined.
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Users who want to use Xen with statically partitioned domains, can provide
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the fixed non zero load address and start address for the dom0/domU kernel.
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The load address and start address specified by the user in the header must
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be within the memory region allocated by Xen.
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Also, it is to be noted that if user provides the legacy image header on
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top of zImage or Image header, then Xen uses the attributes of legacy
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image header to determine the load address, entry point, etc.
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Firmware/bootloader requirements
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--------------------------------
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Xen relies on some settings the firmware has to configure in EL3 before starting Xen.
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* Xen must be entered in NS EL2 mode
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* The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.
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[1] linux/Documentation/arm/booting.rst
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Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/booting.rst
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[2] linux/Documentation/arm64/booting.rst
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Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.rst
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[3] legacy format header
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Latest version: https://source.denx.de/u-boot/u-boot/-/blob/master/include/image.h#L315
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https://linux.die.net/man/1/mkimage
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