linux-kernel - Re: [PATCH] Drivers: hv: vmbus: Remove the per-CPU post_msg

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Date:   Mon, 10 Apr 2023 09:58:54 +0530
From:   Jinank Jain <jinankjain@...ux.microsoft.com>
To:     Dexuan Cui <decui@...rosoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        mikelley@...rosoft.com
Subject: Re: [PATCH] Drivers: hv: vmbus: Remove the per-CPU post_msg_page

Reviewed-by: Jinank Jain <jinankjain@...ux.microsoft.com>

On 4/9/2023 3:04 AM, Dexuan Cui wrote:
> The post_msg_page was introduced in 2014 in
> commit b29ef3546aec ("Drivers: hv: vmbus: Cleanup hv_post_message()")
>
> Commit 68bb7bfb7985 ("X86/Hyper-V: Enable IPI enlightenments") introduced
> the hyperv_pcpu_input_arg in 2018, which can be used in hv_post_message().
>
> Remove post_msg_page to simplify the code a little bit.
>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
>   drivers/hv/hv.c           | 20 +++++---------------
>   drivers/hv/hyperv_vmbus.h |  4 ----
>   2 files changed, 5 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 8b0dd8e5244d7..30bf122a502ae 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -84,14 +84,15 @@ int hv_post_message(union hv_connection_id connection_id,
>   		  void *payload, size_t payload_size)
>   {
>   	struct hv_input_post_message *aligned_msg;
> -	struct hv_per_cpu_context *hv_cpu;
> +	unsigned long flags;
>   	u64 status;
>   
>   	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT)
>   		return -EMSGSIZE;
>   
> -	hv_cpu = get_cpu_ptr(hv_context.cpu_context);
> -	aligned_msg = hv_cpu->post_msg_page;
> +	local_irq_save(flags);
> +
> +	aligned_msg = *this_cpu_ptr(hyperv_pcpu_input_arg);
>   	aligned_msg->connectionid = connection_id;
>   	aligned_msg->reserved = 0;
>   	aligned_msg->message_type = message_type;
> @@ -106,11 +107,7 @@ int hv_post_message(union hv_connection_id connection_id,
>   		status = hv_do_hypercall(HVCALL_POST_MESSAGE,
>   				aligned_msg, NULL);
>   
> -	/* Preemption must remain disabled until after the hypercall
> -	 * so some other thread can't get scheduled onto this cpu and
> -	 * corrupt the per-cpu post_msg_page
> -	 */
> -	put_cpu_ptr(hv_cpu);
> +	local_irq_restore(flags);
>   
>   	return hv_result(status);
>   }
> @@ -162,12 +159,6 @@ int hv_synic_alloc(void)
>   				goto err;
>   			}
>   		}
> -
> -		hv_cpu->post_msg_page = (void *)get_zeroed_page(GFP_ATOMIC);
> -		if (hv_cpu->post_msg_page == NULL) {
> -			pr_err("Unable to allocate post msg page\n");
> -			goto err;
> -		}
>   	}
>   
>   	return 0;
> @@ -190,7 +181,6 @@ void hv_synic_free(void)
>   
>   		free_page((unsigned long)hv_cpu->synic_event_page);
>   		free_page((unsigned long)hv_cpu->synic_message_page);
> -		free_page((unsigned long)hv_cpu->post_msg_page);
>   	}
>   
>   	kfree(hv_context.hv_numa_map);
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index dc673edf053c3..d8322049ecd08 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -122,10 +122,6 @@ enum {
>   struct hv_per_cpu_context {
>   	void *synic_message_page;
>   	void *synic_event_page;
> -	/*
> -	 * buffer to post messages to the host.
> -	 */
> -	void *post_msg_page;
>   
>   	/*
>   	 * Starting with win8, we can take channel interrupts on any CPU;