From 18f3976fdb5da2ba9572845e6f7dfb58652871ea Mon Sep 17 00:00:00 2001 From: Alexandru Elisei Date: Mon, 25 Apr 2022 12:44:44 +0100 Subject: 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 Reviewed-by: Marc Zyngier Link: https://lore.kernel.org/r/20220425114444.368693-6-alexandru.elisei@arm.com Signed-off-by: Catalin Marinas --- Documentation/virt/kvm/api.rst | 2 ++ 1 file changed, 2 insertions(+) (limited to 'Documentation/virt/kvm') diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 85c7abc51af5..ecd70d99f3e0 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5713,6 +5713,8 @@ affect the device's behavior. Current defined flags:: #define KVM_RUN_X86_SMM (1 << 0) /* x86, set if bus lock detected in VM */ #define KVM_RUN_BUS_LOCK (1 << 1) + /* arm64, set for KVM_EXIT_DEBUG */ + #define KVM_DEBUG_ARCH_HSR_HIGH_VALID (1 << 0) :: -- cgit v1.2.3