linux-kernel - [RESPIN PATCH] irqchip/gic-v3-its:Fix GICv4.1 needless VSYNC after unmap VPE

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Date: Wed, 3 Apr 2024 08:35:56 +0000
From: t00849498 <tangnianyao@...wei.com>
To: <maz@...nel.org>, <tglx@...utronix.de>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
CC: <guoyang2@...wei.com>, <wangwudi@...ilicon.com>, <tangnianyao@...wei.com>
Subject: [RESPIN PATCH] irqchip/gic-v3-its:Fix GICv4.1 needless VSYNC after unmap VPE

From: Nianyao Tang <tangnianyao@...wei.com>

Quote from GIC spec 5.3.19, a VMAPP with {V, Alloc}=={0, x}
is self-synchronizing, This means the ITS command queue does not
show the command as consumed until all of its effects are completed.

We don't need VSYNC to guarantee unmap finish. And VSYNC after unmap VPE
will reach an invalid vpe table entry, which may trigger exception
like SError or RAS. Let's fix it.

Signed-off-by: Nianyao Tang <tangnianyao@...wei.com>
---
 drivers/irqchip/irq-gic-v3-its.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index fca888b36680..2a537cbfcb07 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -786,6 +786,7 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
 					   struct its_cmd_block *cmd,
 					   struct its_cmd_desc *desc)
 {
+	struct its_vpe *vpe = valid_vpe(its, desc->its_vmapp_cmd.vpe);
 	unsigned long vpt_addr, vconf_addr;
 	u64 target;
 	bool alloc;
@@ -798,6 +799,11 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
 		if (is_v4_1(its)) {
 			alloc = !atomic_dec_return(&desc->its_vmapp_cmd.vpe->vmapp_count);
 			its_encode_alloc(cmd, alloc);
+			/*
+			 * Unmapping a VPE is self-synchronizing on GICv4.1,
+			 * no need to issue a VSYNC.
+			 */
+			vpe = NULL;
 		}
 
 		goto out;
@@ -832,7 +838,7 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
 out:
 	its_fixup_cmd(cmd);
 
-	return valid_vpe(its, desc->its_vmapp_cmd.vpe);
+	return vpe;
 }
 
 static struct its_vpe *its_build_vmapti_cmd(struct its_node *its,
-- 
2.30.0