On Wed, Jun 15, 2022 at 06:57:06PM +0000, Raghavendra Rao Ananta wrote:
> The selftests, when built with newer versions of clang, is found
> to have over optimized guests' ucall() function, and eliminating
> the stores for uc.cmd (perhaps due to no immediate readers). This
> resulted in the userspace side always reading a value of '0', and
> causing multiple test failures.
>
> As a result, prevent the compiler from optimizing the stores in
> ucall() with WRITE_ONCE().
>
> Suggested-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
> Suggested-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> ---
> tools/testing/selftests/kvm/lib/aarch64/ucall.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/aarch64/ucall.c b/tools/testing/selftests/kvm/lib/aarch64/ucall.c
> index e0b0164e9af8..be1d9728c4ce 100644
> --- a/tools/testing/selftests/kvm/lib/aarch64/ucall.c
> +++ b/tools/testing/selftests/kvm/lib/aarch64/ucall.c
> @@ -73,20 +73,19 @@ void ucall_uninit(struct kvm_vm *vm)
>
> void ucall(uint64_t cmd, int nargs, ...)
> {
> - struct ucall uc = {
> - .cmd = cmd,
> - };
> + struct ucall uc = {};
> va_list va;
> int i;
>
> + WRITE_ONCE(uc.cmd, cmd);
> nargs = nargs <= UCALL_MAX_ARGS ? nargs : UCALL_MAX_ARGS;
>
> va_start(va, nargs);
> for (i = 0; i < nargs; ++i)
> - uc.args[i] = va_arg(va, uint64_t);
> + WRITE_ONCE(uc.args[i], va_arg(va, uint64_t));
> va_end(va);
>
> - *ucall_exit_mmio_addr = (vm_vaddr_t)&uc;
> + WRITE_ONCE(*ucall_exit_mmio_addr, (vm_vaddr_t)&uc);
> }
>
> uint64_t get_ucall(struct kvm_vm *vm, uint32_t vcpu_id, struct ucall *uc)
> --
> 2.36.1.476.g0c4daa206d-goog
>
Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
Thanks,
drew
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