RE: [PATCH v4 0/4] KVM: arm64: BUG FIX: Correctly handle zero register transfers

[Pavel Fedin <p.fedin@samsung.com>]

 Hello!

> FYI, I tried writing test cases for this issue with kvm-unit-tests. The
> issue didn't reproduce for me. It's quite possible my test cases are
> flawed, so I'm not making any claims about the validity of the series

 This is indeed very interesting, so i'll take a look at it.
 For now i've just only took a quick glance at the code, and i have at least one suggestion. Could you happen to have sp == 0 in
check_xzr_sysreg()? In this case it will magically work.
 Also, you could try to write a test which tries to overwrite xzr. Something like:

volatile int *addr1;
volatile int *addr2;

asm volatile("str %3, [%1]\n\t"
             "ldr wzr, [%1]\n\t"
             "str wzr, [%2]\n\t",
             "ldr %0, [%2]\n\t"
             :"=r"(res):"r"(addr1), "r"(addr2), "r"(some_nonzero_val):"memory");

 Then check for res == some_nonzero_val. If they are equal, you've got the bug :)

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia