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Ayan Kumar Halder
78e93e6e57
Currently, kernel_uimage_probe() does not read the load/entry point address set in the uImge header. Thus, info->zimage.start is 0 (default value). This causes, kernel_zimage_place() to treat the binary (contained within uImage) as position independent executable. Thus, it loads it at an incorrect address. The correct approach would be to read "uimage.load" and set info->zimage.start. This will ensure that the binary is loaded at the correct address. Also, read "uimage.ep" and set info->entry (ie kernel entry address). If user provides load address (ie "uimage.load") as 0x0, then the image is treated as position independent executable. Xen can load such an image at any address it considers appropriate. A position independent executable cannot have a fixed entry point address. This behavior is applicable for both arm32 and arm64 platforms. Earlier for arm32 and arm64 platforms, Xen was ignoring the load and entry point address set in the uImage header. With this commit, Xen will use them. This makes the behavior of Xen consistent with uboot for uimage headers. Users who want to use Xen with statically partitioned domains, can provide non zero load address and entry address for the dom0/domU kernel. It is required that the load and entry address provided must be within the memory region allocated by Xen. A deviation from uboot behaviour is that we consider load address == 0x0, to denote that the image supports position independent execution. This is to make the behavior consistent across uImage and zImage. Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com> [stefano: minor doc improvement] Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
76 lines
2.8 KiB
Plaintext
76 lines
2.8 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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Known limitation: compressed kernels with a uboot headers are not
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working.
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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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