linux-kernel - [PATCH 2/2] xen/swiotlb: check if the swiotlb has already been initialized

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Message-Id: <20210511174142.12742-2-sstabellini@kernel.org>
Date:   Tue, 11 May 2021 10:41:42 -0700
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     xen-devel@...ts.xenproject.org
Cc:     sstabellini@...nel.org, hch@....de, linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano.stabellini@...inx.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com
Subject: [PATCH 2/2] xen/swiotlb: check if the swiotlb has already been initialized

From: Stefano Stabellini <stefano.stabellini@...inx.com>

xen_swiotlb_init calls swiotlb_late_init_with_tbl, which fails with
-ENOMEM if the swiotlb has already been initialized.

Add an explicit check io_tlb_default_mem != NULL at the beginning of
xen_swiotlb_init. If the swiotlb is already initialized print a warning
and return -EEXIST.

On x86, the error propagates.

On ARM, we don't actually need a special swiotlb buffer (yet), any
buffer would do. So ignore the error and continue.

CC: boris.ostrovsky@...cle.com
CC: jgross@...e.com
Signed-off-by: Stefano Stabellini <stefano.stabellini@...inx.com>
---
 arch/arm/xen/mm.c         | 8 +++++++-
 drivers/xen/swiotlb-xen.c | 5 +++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 223b1151fd7d..a7e54a087b80 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -138,9 +138,15 @@ void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order)
 static int __init xen_mm_init(void)
 {
 	struct gnttab_cache_flush cflush;
+	int rc;
+
 	if (!xen_swiotlb_detect())
 		return 0;
-	xen_swiotlb_init();
+
+	rc = xen_swiotlb_init();
+	/* we can work with the default swiotlb */
+	if (rc < 0 && rc != -EEXIST)
+		return rc;
 
 	cflush.op = 0;
 	cflush.a.dev_bus_addr = 0;
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 4c89afc0df62..6412d59ce7f8 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -164,6 +164,11 @@ int __ref xen_swiotlb_init(void)
 	int rc = -ENOMEM;
 	char *start;
 
+	if (io_tlb_default_mem != NULL) {
+		printk(KERN_WARNING "Xen-SWIOTLB: swiotlb buffer already initialized\n");
+		return -EEXIST;
+	}
+
 retry:
 	m_ret = XEN_SWIOTLB_ENOMEM;
 	order = get_order(bytes);
-- 
2.17.1