Re: [V3 10/11] KVM: selftests: Add ucall pool based implementation

Vishal Annapurve
2022-08-19T19:28:06Z

On Wed, Aug 10, 2022 at 8:20 AM Peter Gonda <pgonda@google.com> wrote:
> ...
> +
> +static struct ucall *ucall_alloc(void)
> +{
> + struct ucall *uc = NULL;
> + int i;
> +
> + if (!use_ucall_pool)
> + goto out;
> +
> + for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> + if (!atomic_test_and_set_bit(i, ucall_pool->in_use)) {
> + uc = &ucall_pool->ucalls[i];
> + memset(uc->args, 0, sizeof(uc->args));
> + break;
> + }
> + }
> +out:
> + return uc;
> +}
> +
> +static inline size_t uc_pool_idx(struct ucall *uc)
> +{
> + return uc->hva - ucall_pool->ucalls;
> +}
> +
> +static void ucall_free(struct ucall *uc)
> +{
> + if (!use_ucall_pool)
> + return;
> +
> + clear_bit(uc_pool_idx(uc), ucall_pool->in_use);
> +}
>
> void ucall(uint64_t cmd, int nargs, ...)
> {
> - struct ucall uc = {};
> + struct ucall *uc;
> + struct ucall tmp = {};

This steps seems to result in generating instructions that need SSE
support on x86:
struct ucall tmp = {};
movaps %xmm0,0x20(%rsp)
movaps %xmm0,0x30(%rsp)
movaps %xmm0,0x40(%rsp)
movaps %xmm0,0x50(%rsp)

This initialization will need proper compilation flags to generate
instructions according to VM configuration.

> va_list va;
> int i;
>
> - WRITE_ONCE(uc.cmd, cmd);
> + uc = ucall_alloc();
> + if (!uc)
> + uc = &tmp;
> +
> + WRITE_ONCE(uc->cmd, cmd);
>
> nargs = min(nargs, UCALL_MAX_ARGS);
>
> va_start(va, nargs);
> for (i = 0; i < nargs; ++i)
> - WRITE_ONCE(uc.args[i], va_arg(va, uint64_t));
> + WRITE_ONCE(uc->args[i], va_arg(va, uint64_t));
> va_end(va);
>
> - ucall_arch_do_ucall((vm_vaddr_t)&uc);
> ...