linux-kernel - [PATCH v7 1/9] swiotlb: bail out of swiotlb_init

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Message-Id: <2d7e1823e264aa1990899cc95736e78e1ec21084.1690871004.git.petr.tesarik.ext@huawei.com>
Date:   Tue,  1 Aug 2023 08:23:56 +0200
From:   Petr Tesarik <petrtesarik@...weicloud.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Petr Tesarik <petr.tesarik.ext@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        James Seo <james@...iv.tech>,
        James Clark <james.clark@....com>,
        Kees Cook <keescook@...omium.org>,
        xen-devel@...ts.xenproject.org (moderated list:XEN HYPERVISOR ARM),
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM PORT),
        linux-kernel@...r.kernel.org (open list),
        linux-mips@...r.kernel.org (open list:MIPS),
        iommu@...ts.linux.dev (open list:XEN SWIOTLB SUBSYSTEM),
        linux-mm@...ck.org (open list:SLAB ALLOCATOR)
Cc:     Roberto Sassu <roberto.sassu@...weicloud.com>, petr@...arici.cz
Subject: [PATCH v7 1/9] swiotlb: bail out of swiotlb_init_late() if swiotlb is already allocated

From: Petr Tesarik <petr.tesarik.ext@...wei.com>

If swiotlb is allocated, immediately return 0, so callers do not have to
check io_tlb_default_mem.nslabs explicitly.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@...wei.com>
---
 arch/arm/xen/mm.c    | 10 ++++------
 kernel/dma/swiotlb.c |  3 +++
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 3d826c0b5fee..882cd70c7a2f 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -125,12 +125,10 @@ static int __init xen_mm_init(void)
 		return 0;
 
 	/* we can work with the default swiotlb */
-	if (!io_tlb_default_mem.nslabs) {
-		rc = swiotlb_init_late(swiotlb_size_or_default(),
-				       xen_swiotlb_gfp(), NULL);
-		if (rc < 0)
-			return rc;
-	}
+	rc = swiotlb_init_late(swiotlb_size_or_default(),
+			       xen_swiotlb_gfp(), NULL);
+	if (rc < 0)
+		return rc;
 
 	cflush.op = 0;
 	cflush.a.dev_bus_addr = 0;
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 1c0a49e6685a..ee57fd9949dc 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -384,6 +384,9 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
 	bool retried = false;
 	int rc = 0;
 
+	if (io_tlb_default_mem.nslabs)
+		return 0;
+
 	if (swiotlb_force_disable)
 		return 0;
 
-- 
2.25.1