linux-kernel - [PATCH v2 1/4] swiotlb-xen: ensure to issue well-formed XENMEM

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Date:   Fri, 17 Sep 2021 12:45:49 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "hch@....de" <hch@....de>, Konrad Wilk <konrad.wilk@...cle.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: [PATCH v2 1/4] swiotlb-xen: ensure to issue well-formed
 XENMEM_exchange requests

While the hypervisor hasn't been enforcing this, we would still better
avoid issuing requests with GFNs not aligned to the requested order.
Instead of altering the value also in the call to panic(), drop it
there for being static and hence easy to determine without being part
of the panic message.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
---
I question how useful it is to wrap "bytes" in PAGE_ALIGN(), when it is
a multiple of a segment's size anyway (or at least was supposed to be,
prior to "swiotlb-xen: maintain slab count properly"). But that's
perhaps yet another separate patch.
---
v2: Drop logging of alignment. Wrap lines.

--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -230,10 +230,11 @@ retry:
 	/*
 	 * Get IO TLB memory from any location.
 	 */
-	start = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
+	start = memblock_alloc(PAGE_ALIGN(bytes),
+			       IO_TLB_SEGSIZE << IO_TLB_SHIFT);
 	if (!start)
-		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
-		      __func__, PAGE_ALIGN(bytes), PAGE_SIZE);
+		panic("%s: Failed to allocate %lu bytes\n",
+		      __func__, PAGE_ALIGN(bytes));
 
 	/*
 	 * And replace that memory with pages under 4GB.