Re: [PATCH v5 1/9] KVM: PPC: selftests: add support for powerpc

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] kvm: selftests: missing save/restore of %r1 and %r2 in ex_regs
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commit 2e259a0445aae14d6a7262b100f4677735b2217f
Author: Nicholas Piggin <npiggin@gmail.com>

KVM: PPC: selftests: add support for powerpc

This commit implements KVM selftests support for powerpc (Book3S-64). It
provides virtual memory implementation for the radix MMU, ucalls using an
unsupported PAPR hcall number, and real-mode guest interrupts.

Link: https://lore.kernel.org/linuxppc-dev/cover.1781093720.git.ritesh.list@gmail.com/

> diff --git a/tools/testing/selftests/kvm/lib/powerpc/handlers.S b/tools/testing/selftests/kvm/lib/powerpc/handlers.S
> new file mode 100644
> index 0000000000000..b860f6a520a13
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/lib/powerpc/handlers.S

[ ... ]

> +virt_handle_interrupt:
> +	stdu	%r1,-INT_FRAME_SIZE(%r1)
> +	mr	%r3,%r31

[ ... ]

> +	mtxer	%r8
> +	mtcr	%r9
> +reg=4
> +	ld	%r0,(0*8)(%r31)
> +	ld	%r3,(3*8)(%r31)
> +.rept 28
> +	ld	reg,(reg*8)(%r31)
> +	reg=reg+1
> +.endr

[Severity: Medium]
Does this restore loop in virt_handle_interrupt intentionally skip restoring
%r1 (stack pointer) and %r2 (TOC base)?

Because the loop starts at reg=4 and ends at %r31, any changes made to the
stack pointer or TOC base by the C exception handler in the ex_regs
structure will be silently ignored when returning to the guest.

> +	addi	%r1,%r1,INT_FRAME_SIZE
> +	rfid
> +
> +virt_handle_interrupt_p:
> +	.llong virt_handle_interrupt
> +
> +handle_interrupt:
> +reg=4
> +.rept 28
> +	std	reg,(reg*8)(%r13)
> +	reg=reg+1
> +.endr

[Severity: Medium]
Similarly, does handle_interrupt skip saving %r1 and %r2 into the ex_regs
structure before routing to the C handler? 

If a selftest takes an exception and attempts to inspect the interrupted
stack or TOC by reading regs->gprs[1] or regs->gprs[2], won't it receive
uninitialized values instead of the actual register states?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1790101179.git.ritesh.list@gmail.com?part=1