linux/arch/arm64
Alexandru Elisei 18f3976fdb KVM: arm64: uapi: Add kvm_debug_exit_arch.hsr_high
When userspace is debugging a VM, the kvm_debug_exit_arch part of the
kvm_run struct contains arm64 specific debug information: the ESR_EL2
value, encoded in the field "hsr", and the address of the instruction
that caused the exception, encoded in the field "far".

Linux has moved to treating ESR_EL2 as a 64-bit register, but unfortunately
kvm_debug_exit_arch.hsr cannot be changed because that would change the
memory layout of the struct on big endian machines:

Current layout:			| Layout with "hsr" extended to 64 bits:
				|
offset 0: ESR_EL2[31:0] (hsr)   | offset 0: ESR_EL2[61:32] (hsr[61:32])
offset 4: padding		| offset 4: ESR_EL2[31:0]  (hsr[31:0])
offset 8: FAR_EL2[61:0] (far)	| offset 8: FAR_EL2[61:0]  (far)

which breaks existing code.

The padding is inserted by the compiler because the "far" field must be
aligned to 8 bytes (each field must be naturally aligned - aapcs64 [1],
page 18), and the struct itself must be aligned to 8 bytes (the struct must
be aligned to the maximum alignment of its fields - aapcs64, page 18),
which means that "hsr" must be aligned to 8 bytes as it is the first field
in the struct.

To avoid changing the struct size and layout for the existing fields, add a
new field, "hsr_high", which replaces the existing padding. "hsr_high" will
be used to hold the ESR_EL2[61:32] bits of the register. The memory layout,
both on big and little endian machine, becomes:

offset 0: ESR_EL2[31:0]  (hsr)
offset 4: ESR_EL2[61:32] (hsr_high)
offset 8: FAR_EL2[61:0]  (far)

The padding that the compiler inserts for the current struct layout is
unitialized. To prevent an updated userspace running on an old kernel
mistaking the padding for a valid "hsr_high" value, add a new flag,
KVM_DEBUG_ARCH_HSR_HIGH_VALID, to kvm_run->flags to let userspace know that
"hsr_high" holds a valid ESR_EL2[61:32] value.

[1] https://github.com/ARM-software/abi-aa/releases/download/2021Q3/aapcs64.pdf

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220425114444.368693-6-alexandru.elisei@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2022-04-29 19:26:27 +01:00
..
boot arm64: dts: qcom/sdm845-shift-axolotl: Fix boolean properties with values 2022-04-14 22:52:17 +02:00
configs ARM: DT updates for 5.18 2022-03-23 18:37:22 -07:00
crypto crypto: arm64 - cleanup comments 2022-03-09 15:12:32 +12:00
hyperv arm64: hyperv: Initialize hypervisor on boot 2021-08-04 16:54:36 +00:00
include KVM: arm64: uapi: Add kvm_debug_exit_arch.hsr_high 2022-04-29 19:26:27 +01:00
kernel arm64: Treat ESR_ELx as a 64-bit register 2022-04-29 19:26:27 +01:00
kvm KVM: arm64: uapi: Add kvm_debug_exit_arch.hsr_high 2022-04-29 19:26:27 +01:00
lib Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2022-03-21 16:02:36 -07:00
mm arm64: Treat ESR_ELx as a 64-bit register 2022-04-29 19:26:27 +01:00
net kasan, arm64: don't tag executable vmalloc allocations 2022-03-24 19:06:48 -07:00
tools Merge branch 'for-next/spectre-bhb' into for-next/core 2022-03-14 19:08:31 +00:00
xen xen: allow pv-only hypercalls only with CONFIG_XEN_PV 2021-11-02 08:11:01 -05:00
Kbuild kbuild: use more subdir- for visiting subdirectories while cleaning 2021-10-24 13:49:46 +09:00
Kconfig Char/Misc and other driver updates for 5.18-rc1 2022-03-28 12:27:35 -07:00
Kconfig.debug
Kconfig.platforms ARM: DT updates for 5.18 2022-03-23 18:37:22 -07:00
Makefile arm64/xor: use EOR3 instructions when available 2021-12-14 12:14:26 +00:00