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

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Message-Id: <1740611284-27506-8-git-send-email-nunodasneves@linux.microsoft.com>
Date: Wed, 26 Feb 2025 15:08:01 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
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Subject: [PATCH v5 07/10] Drivers: hv: Introduce per-cpu event ring tail

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@...ux.microsoft.com>
Reviewed-by: Wei Liu <wei.liu@...nel.org>
---
 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