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Dirk Behme
7d59c1a918
Add a section about what the firmware should do in EL3 before starting Xen. E.g guest will use HVC instruction to issue hypercall. As this can be set only at EL3, i.e. outside Xen, document this boot requirement. Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
42 lines
1.4 KiB
Plaintext
42 lines
1.4 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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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.HCR (resp. SCR.HCE for 32-bit ARM) must be set to 1.
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[1] linux/Documentation/arm/Booting
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Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/Booting
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[2] linux/Documentation/arm64/booting.txt
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Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.txt
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