Re: [PATCH v4 07/10] KVM: selftests: Support multiple vCPUs in demand paging test

Andrew Jones
2020-01-24T10:16:49Z

On Thu, Jan 23, 2020 at 10:04:33AM -0800, Ben Gardon wrote:
> Most VMs have multiple vCPUs, the concurrent execution of which has a
> substantial impact on demand paging performance. Add an option to create
> multiple vCPUs to each access disjoint regions of memory.
>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
> .../selftests/kvm/demand_paging_test.c | 255 ++++++++++++------
> 1 file changed, 172 insertions(+), 83 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index 9e2a5f7dfa140..2002032df32cc 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -24,8 +24,6 @@
> #include "kvm_util.h"
> #include "processor.h"
>
> -#define VCPU_ID 1
> -
> /* The memory slot index demand page */
> #define TEST_MEM_SLOT_INDEX 1
>
> @@ -34,6 +32,14 @@
>
> #define DEFAULT_GUEST_TEST_MEM_SIZE (1 << 30) /* 1G */
>
> +#ifdef PRINT_PER_VCPU_UPDATES
> +#define PER_VCPU_DEBUG(...) DEBUG(__VA_ARGS__)
> +#else
> +#define PER_VCPU_DEBUG(...)
> +#endif
> +
> +#define MAX_VCPUS 512
> +
> /*
> * Guest/Host shared variables. Ensure addr_gva2hva() and/or
> * sync_global_to/from_guest() are used when accessing from
> @@ -67,18 +73,25 @@ struct vcpu_args {
> struct kvm_vm *vm;
> };
>
> -static struct vcpu_args vcpu_args;
> +static struct vcpu_args vcpu_args[MAX_VCPUS];
>
> /*
> * Continuously write to the first 8 bytes of each page in the demand paging
> * memory region.
> */
> -static void guest_code(void)
> +static void guest_code(uint32_t vcpu_id)
> {
> - uint64_t gva = vcpu_args.gva;
> - uint64_t pages = vcpu_args.pages;
> + uint64_t gva;
> + uint64_t pages;
> int i;
>
> + /* Return to signal error if vCPU args data structure is courrupt. */
> + if (vcpu_args[vcpu_id].vcpu_id != vcpu_id)
> + return;

This should be GUEST_ASSERT(vcpu_args[vcpu_id].vcpu_id == vcpu_id), which
will do a UCALL_ABORT when it fails. Otherwise we're returning to where?
Likely we'll get an exception of some sort when we return to nothing,
but that's not a very clean way to die.

Thanks,
drew