On Wed, Feb 14, 2024 at 05:00:04PM -0800, Sean Christopherson wrote:
> Add forced emulation of MOV and LOCK CMPXCHG instructions in the dirty log
> test's guest code to verify that KVM's emulator marks pages dirty as
> expected (and obviously to verify the emulator works at all). In the long
> term, the guest code would ideally hammer more of KVM's emulator, but for
> starters, cover the two major paths: writes and atomics.
>
> To minimize #ifdeffery, wrap only the related code that is x86 specific,
> unnecessariliy synchronizing an extra boolean to the guest is far from the
> end of the world.
Meh, I wouldn't say the end result in guest_write_memory() is that
pretty. Just ifdef the whole function and provide a generic implementation
for the other architectures.
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> tools/testing/selftests/kvm/dirty_log_test.c | 36 ++++++++++++++++++--
> 1 file changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index eaad5b20854c..ff1d1c7f05d8 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -92,6 +92,29 @@ static uint64_t guest_test_phys_mem;
> */
> static uint64_t guest_test_virt_mem = DEFAULT_GUEST_TEST_MEM;
>
> +static bool is_forced_emulation_enabled;
> +
> +static void guest_write_memory(uint64_t *mem, uint64_t val, uint64_t rand)
> +{
> +#ifdef __x86_64__
> + if (is_forced_emulation_enabled && (rand & 1)) {
> + if (rand & 2) {
Can't you invert the logic and drop a level of indentation?
if (!(is_forced_emulation_enabled && (rand & 1))) {
*mem = val;
} else if (rand & 2) {
movq
} else {
cmpxchg8b
}
> + __asm__ __volatile__(KVM_FEP "movq %1, %0"
> + : "+m" (*mem)
> + : "r" (val) : "memory");
> + } else {
> + uint64_t __old = READ_ONCE(*mem);
> +
> + __asm__ __volatile__(KVM_FEP LOCK_PREFIX "cmpxchgq %[new], %[ptr]"
> + : [ptr] "+m" (*mem), [old] "+a" (__old)
> + : [new]"r" (val) : "memory", "cc");
> + }
> + } else
> +#endif
> +
> + *mem = val;
> +}
> +
--
Thanks,
Oliver
