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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tsl2q-0000000BkNM-0D6K; Thu, 13 Mar 2025 16:04:28 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tskuy-0000000Big5-2scK for linux-arm-kernel@lists.infradead.org; Thu, 13 Mar 2025 15:56:21 +0000 Received: from [10.0.0.114] (c-67-182-156-199.hsd1.wa.comcast.net [67.182.156.199]) by linux.microsoft.com (Postfix) with ESMTPSA id D11BC2033428; Thu, 13 Mar 2025 08:56:18 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com D11BC2033428 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1741881379; bh=LKcLmiNNi+InVHi7szN5VvzBxGJ1ZV4koF9yq2Mj56E=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=qSExLbcPE0nUhHTgfvpnil9EmZuIMMSMVTDhe2uERE4lfle83/MgTG/KdG0Y29IBw dFMT3xgTbiqrd2QyplZgYbBU+EfyIBNbGBcD8Xh1V7EdpBIjZR5ZNZ4gTi/C/AsMs1 j4PyUkiW1dba5UiyKnL1QfdZk2Ow5UZhErEHVqKU= Message-ID: <6ba21efb-7065-44d7-9cee-265a0c137f0c@linux.microsoft.com> Date: Thu, 13 Mar 2025 08:56:18 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 07/10] Drivers: hv: Introduce per-cpu event ring tail To: Tianyu Lan Cc: linux-hyperv@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-acpi@vger.kernel.org, kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, mhklinux@outlook.com, decui@microsoft.com, catalin.marinas@arm.com, will@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, daniel.lezcano@linaro.org, joro@8bytes.org, robin.murphy@arm.com, arnd@arndb.de, jinankjain@linux.microsoft.com, muminulrussell@gmail.com, skinsburskii@linux.microsoft.com, mrathor@linux.microsoft.com, ssengar@linux.microsoft.com, apais@linux.microsoft.com, Tianyu.Lan@microsoft.com, stanislav.kinsburskiy@gmail.com, gregkh@linuxfoundation.org, vkuznets@redhat.com, prapal@linux.microsoft.com, muislam@microsoft.com, anrayabh@linux.microsoft.com, rafael@kernel.org, lenb@kernel.org, corbet@lwn.net References: <1740611284-27506-1-git-send-email-nunodasneves@linux.microsoft.com> <1740611284-27506-8-git-send-email-nunodasneves@linux.microsoft.com> <5e3e8c30-912c-4fe3-bfac-1ae21242473b@linux.microsoft.com> Content-Language: en-US From: Nuno Das Neves In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250313_085620_777700_A791415D X-CRM114-Status: GOOD ( 22.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 3/13/2025 12:34 AM, Tianyu Lan wrote: > On Thu, Mar 13, 2025 at 3:45 AM Nuno Das Neves > wrote: >> >> On 3/10/2025 6:01 AM, Tianyu Lan wrote: >>> On Thu, Feb 27, 2025 at 7:09 AM Nuno Das Neves >>> 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 >>>> Reviewed-by: Wei Liu >>> >>> It's better to expose a function to check the tail instead of exposing >>> hv_synic_eventring_tail directly. >>> >> What is the advantage of using a function for this? We need to both set >> and get the tail. > > We may add lock or check to avoid race conditions and this depends on the > user case. This is why I want to see how mshv driver uses it. > >> >>> BTW, how does mshv driver use hv_synic_eventring_tail? Which patch >>> uses it in this series? >>> >> This variable stores indices into the synic eventring page (one for each >> SINT, and per-cpu). Each SINT has a ringbuffer of u32 messages. The tail >> index points to the latest one. >> >> This is only used for doorbell messages today. The message in this case is >> a port number which is used to lookup and invoke a callback, which signals >> ioeventfd(s), to notify the VMM of a guest MMIO write. >> >> It is used in patch 10. > > I found "extern u8 __percpu **hv_synic_eventring_tail;" in the > drivers/hv/mshv_root.h of patch 10. > I seem to miss the code to use it. > > +int hv_call_unmap_stat_page(enum hv_stats_object_type type, > + const union hv_stats_object_identity *identity); > +int hv_call_modify_spa_host_access(u64 partition_id, struct page **pages, > + u64 page_struct_count, u32 host_access, > + u32 flags, u8 acquire); > + > +extern struct mshv_root mshv_root; > +extern enum hv_scheduler_type hv_scheduler_type; > +extern u8 __percpu **hv_synic_eventring_tail; > + > +#endif /* _MSHV_ROOT_H_ */ > It is used in mshv_synic.c in synic_event_ring_get_queued_port(): diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c new file mode 100644 index 000000000000..e7782f92e339 --- /dev/null +++ b/drivers/hv/mshv_synic.c @@ -0,0 +1,665 @@ +static u32 synic_event_ring_get_queued_port(u32 sint_index) +{ + struct hv_synic_event_ring_page **event_ring_page; + volatile struct hv_synic_event_ring *ring; + struct hv_synic_pages *spages; + u8 **synic_eventring_tail; + u32 message; + u8 tail; + + spages = this_cpu_ptr(mshv_root.synic_pages); + event_ring_page = &spages->synic_event_ring_page; + synic_eventring_tail = (u8 **)this_cpu_ptr(hv_synic_eventring_tail); + tail = (*synic_eventring_tail)[sint_index];