Re: [PATCH 11/16] hw/arm/highbank: Drop use of secure_board_setup

[Richard Henderson <richard.henderson@linaro.org>]

On 1/28/22 02:46, Peter Maydell wrote:
> Guest code on highbank may make non-PSCI SMC calls in order to
> enable/disable the L2x0 cache controller (see the Linux kernel's
> arch/arm/mach-highbank/highbank.c highbank_l2c310_write_sec()
> function).  The ABI for this is documented in kernel commit
> 8e56130dcb as being borrowed from the OMAP44xx ROM.  The OMAP44xx TRM
> documents this function ID as having no return value and potentially
> trashing all guest registers except SP and PC. For QEMU's purposes
> (where our L2x0 model is a stub and enabling or disabling it doesn't
> affect the guest behaviour) a simple "do nothing" SMC is fine.
> 
> We currently implement this NOP behaviour using a little bit of
> Secure code we run before jumping to the guest kernel, which is
> written by arm_write_secure_board_setup_dummy_smc().  The code sets
> up a set of Secure vectors where the SMC entry point returns without
> doing anything.
> 
> Now that the PSCI SMC emulation handles all SMC calls (setting r0 to
> an error code if the input r0 function identifier is not recognized),
> we can use that default behaviour as sufficient for the highbank
> cache controller call.  (Because the guest code assumes r0 has no
> interesting value on exit it doesn't matter that we set it to the
> error code).  We can therefore delete the highbank board code that
> sets secure_board_setup to true and writes the secure-code bootstub.
> 
> (Note that because the OMAP44xx ABI puts function-identifiers in
> r12 and PSCI uses r0, we only avoid a clash because Linux's code
> happens to put the function-identifier in both registers. But this
> is true also when the kernel is running on real firmware that
> implements both ABIs as far as I can see.)
> 
> This change fixes in passing booting on the 'midway' board model,
> which has been completely broken since we added support for Hyp
> mode to the Cortex-A15 CPU. When we did that boot.c was made to
> start running the guest code in Hyp mode; this includes the
> board_setup hook, which instantly UNDEFs because the NSACR is
> not accessible from Hyp. (Put another way, we never made the
> secure_board_setup hook support cope with Hyp mode.)
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   hw/arm/highbank.c | 8 --------
>   1 file changed, 8 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~