Re: [PATCH v5 07/10] Drivers: hv: Introduce per-cpu event ring tail

[Tianyu Lan <ltykernel@gmail.com>]

On Thu, Feb 27, 2025 at 7:09 AM Nuno Das Neves
<nunodasneves@linux.microsoft.com> wrote:
>
> Add a pointer hv_synic_eventring_tail to track the tail pointer for the
> SynIC event ring buffer for each SINT.
>
> This will be used by the mshv driver, but must be tracked independently
> since the driver module could be removed and re-inserted.
>
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> Reviewed-by: Wei Liu <wei.liu@kernel.org>

It's better to expose a function to check the tail instead of exposing
hv_synic_eventring_tail directly.

BTW, how does mshv driver use hv_synic_eventring_tail? Which patch
uses it in this series?

Thanks.


> ---
>  drivers/hv/hv_common.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 252fd66ad4db..2763cb6d3678 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -68,6 +68,16 @@ static void hv_kmsg_dump_unregister(void);
>
>  static struct ctl_table_header *hv_ctl_table_hdr;
>
> +/*
> + * Per-cpu array holding the tail pointer for the SynIC event ring buffer
> + * for each SINT.
> + *
> + * We cannot maintain this in mshv driver because the tail pointer should
> + * persist even if the mshv driver is unloaded.
> + */
> +u8 __percpu **hv_synic_eventring_tail;
> +EXPORT_SYMBOL_GPL(hv_synic_eventring_tail);
> +
>  /*
>   * Hyper-V specific initialization and shutdown code that is
>   * common across all architectures.  Called from architecture
> @@ -90,6 +100,9 @@ void __init hv_common_free(void)
>
>         free_percpu(hyperv_pcpu_input_arg);
>         hyperv_pcpu_input_arg = NULL;
> +
> +       free_percpu(hv_synic_eventring_tail);
> +       hv_synic_eventring_tail = NULL;
>  }
>
>  /*
> @@ -372,6 +385,11 @@ int __init hv_common_init(void)
>                 BUG_ON(!hyperv_pcpu_output_arg);
>         }
>
> +       if (hv_root_partition()) {
> +               hv_synic_eventring_tail = alloc_percpu(u8 *);
> +               BUG_ON(hv_synic_eventring_tail == NULL);
> +       }
> +
>         hv_vp_index = kmalloc_array(nr_cpu_ids, sizeof(*hv_vp_index),
>                                     GFP_KERNEL);
>         if (!hv_vp_index) {
> @@ -460,6 +478,7 @@ void __init ms_hyperv_late_init(void)
>  int hv_common_cpu_init(unsigned int cpu)
>  {
>         void **inputarg, **outputarg;
> +       u8 **synic_eventring_tail;
>         u64 msr_vp_index;
>         gfp_t flags;
>         const int pgcount = hv_output_page_exists() ? 2 : 1;
> @@ -472,8 +491,8 @@ int hv_common_cpu_init(unsigned int cpu)
>         inputarg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
>
>         /*
> -        * hyperv_pcpu_input_arg and hyperv_pcpu_output_arg memory is already
> -        * allocated if this CPU was previously online and then taken offline
> +        * The per-cpu memory is already allocated if this CPU was previously
> +        * online and then taken offline
>          */
>         if (!*inputarg) {
>                 mem = kmalloc(pgcount * HV_HYP_PAGE_SIZE, flags);
> @@ -485,6 +504,17 @@ int hv_common_cpu_init(unsigned int cpu)
>                         *outputarg = (char *)mem + HV_HYP_PAGE_SIZE;
>                 }
>
> +               if (hv_root_partition()) {
> +                       synic_eventring_tail = (u8 **)this_cpu_ptr(hv_synic_eventring_tail);
> +                       *synic_eventring_tail = kcalloc(HV_SYNIC_SINT_COUNT,
> +                                                       sizeof(u8), flags);
> +
> +                       if (unlikely(!*synic_eventring_tail)) {
> +                               kfree(mem);
> +                               return -ENOMEM;
> +                       }
> +               }
> +
>                 if (!ms_hyperv.paravisor_present &&
>                     (hv_isolation_type_snp() || hv_isolation_type_tdx())) {
>                         ret = set_memory_decrypted((unsigned long)mem, pgcount);
> --
> 2.34.1
>
>


-- 
Thanks
Tianyu Lan