linux-kernel - [PATCH] x86/xen/mmu: Increase MAX_CONTIG

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Message-Id: <20241204171346.458105-1-thierry.escande@vates.tech>
Date: Wed, 04 Dec 2024 17:14:04 +0000
From: "Thierry Escande" <thierry.escande@...es.tech>
To: "Juergen Gross" <jgross@...e.com>, linux-kernel@...r.kernel.org
Cc: sstabellini@...nel.org, oleksandr_tyshchenko@...m.com, jbeulich@...e.com, xen-devel@...ts.xenproject.org
Subject: [PATCH] x86/xen/mmu: Increase MAX_CONTIG_ORDER

With change 9f40ec84a797 (xen/swiotlb: add alignment check for dma
buffers), the driver mpt3sas fails to load because it cannot allocate
its DMA pool for an allocation size of ~2,3 MBytes. This is because the
alignement check added by 9f40ec84a797 fails and
xen_swiotlb_alloc_coherent() ends up calling
xen_create_contiguous_region() with a size order of 10 which is too high
for the current max value.

This patch increases the MAX_CONTIG_ORDER from 9 to 10 (4MB) to allow
such allocations.

Signed-off-by: Thierry Escande <thierry.escande@...es.tech>
---
 arch/x86/xen/mmu_pv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 55a4996d0c04..7f110740e1a2 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -2200,7 +2200,7 @@ void __init xen_init_mmu_ops(void)
 }

 /* Protected by xen_reservation_lock. */
-#define MAX_CONTIG_ORDER 9 /* 2MB */
+#define MAX_CONTIG_ORDER 10 /* 4MB */
 static unsigned long discontig_frames[1<<MAX_CONTIG_ORDER];

 #define VOID_PTE (mfn_pte(0, __pgprot(0)))
-- 
2.45.2