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SubjectRe: [PATCH v3 2/5] KVM: arm64: Compile stacktrace.nvhe.o
On Tue, 07 Jun 2022 17:50:44 +0100,
Kalesh Singh <kaleshsingh@google.com> wrote:
>
> Recompile stack unwinding code for use with the nVHE hypervisor. This is
> a preparatory patch that will allow reusing most of the kernel unwinding
> logic in the nVHE hypervisor.
>
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> Reviewed-by: Mark Brown <broonie@kernel.org>
> ---
>
> Changes in v3:
> - Add Mark's Reviewed-by tag
>
> Changes in v2:
> - Split out refactoring of common unwinding logic into a separate patch,
> per Mark Brown
>
> arch/arm64/include/asm/stacktrace.h | 18 +++++++++-----
> arch/arm64/kernel/stacktrace.c | 37 ++++++++++++++++-------------
> arch/arm64/kvm/hyp/nvhe/Makefile | 3 ++-
> 3 files changed, 35 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index aec9315bf156..f5af9a94c5a6 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -16,12 +16,14 @@
> #include <asm/sdei.h>
>
> enum stack_type {
> - STACK_TYPE_UNKNOWN,
> +#ifndef __KVM_NVHE_HYPERVISOR__
> STACK_TYPE_TASK,
> STACK_TYPE_IRQ,
> STACK_TYPE_OVERFLOW,
> STACK_TYPE_SDEI_NORMAL,
> STACK_TYPE_SDEI_CRITICAL,
> +#endif /* !__KVM_NVHE_HYPERVISOR__ */
> + STACK_TYPE_UNKNOWN,

What is the reason for this reordering? I have the sinking feeling
that this could play badly with the logic that assumes that it is
legal to switch from a lesser stack type to a higher one, and could
allow switching to a duff stack.

I would at least like to see a justification of why this isn't less
safe than the current code.

[...]

> index f9fe4dc21b1f..c0ff0d6fc403 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -14,7 +14,8 @@ lib-objs := $(addprefix ../../../lib/, $(lib-objs))
>
> obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
> hyp-main.o hyp-smp.o psci-relay.o early_alloc.o page_alloc.o \
> - cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o
> + cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o \
> + ../../../kernel/stacktrace.o

This, I positively hate. It is only a marginally better than the
cross-arch references we used to have with arch/arm/kvm. I'd be much
more happy with an include file containing the shared code. It would
also allow the removal of some of the #ifdeferry. Note that this is
the approach that we ended up adopting for the VHE/nVHE split.

Thanks,

M.

--
Without deviation from the norm, progress is not possible.

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