linux-kernel - Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned

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Date:	Fri, 30 Jan 2015 13:54:09 -0800
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-usb@...r.kernel.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all
 pages returned

On Sat, 2015-01-31 at 00:03 +0300, Sergei Shtylyov wrote:
> On 01/30/2015 10:54 PM, Tim Chen wrote:

> >
> >   		return NULL;
> >   	}
> > +	/* round up to full page size */
> > +	size = (((size-1) >> PAGE_SHIFT) + 1) * PAGE_SIZE;
> 
>     This is quite suboptimal formula, we can do without shifts and 
> multiplications (hopefully, still converted to shifts by gcc):
> 
> 	size = (size + ~PAGE_MASK) & PAGE_MASK;

Agree.  I've updated patch below

Thanks.

Tim

--->8---

From: Tim Chen <tim.c.chen@...ux.intel.com>
Subject: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned

Commit d92ef66c4f8f ("x86: make dma_alloc_coherent() return zeroed memory
if CMA is enabled") changed the dma_alloc_coherent page clearance from
using an __GFP_ZERO in page allocation to not setting the flag but doing
an explicit memory clear at the end.

However the memory clear only covered the memory size that
was requested, but may not be up to the full extent of the
last page, if the total pages returned exceed the
memory size requested.  This behavior has caused problem with XHCI
and caused it to hang:

kernel: xhci_hcd 0000:00:14.0: Stopped the command ring failed, maybe the host is dead
kernel: xhci_hcd 0000:00:14.0: Abort command ring failed
kernel: xhci_hcd 0000:00:14.0: HC died; cleaning up
kernel: xhci_hcd 0000:00:14.0: Error while assigning device slot ID
kernel: xhci_hcd 0000:00:14.0: Max number of devices this xHCI host supports is 64.

Other drivers may have similar issue if it assumes that the pages
allocated are completely zeroed.

This patch ensures that the pages returned are fully cleared.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: <stable@...r.kernel.org> # 3.16+

---
 arch/x86/kernel/pci-dma.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index a25e202..e9d8dee 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -125,6 +125,8 @@ again:

 		return NULL;
 	}
+	/* round up to full page size */
+	size = (size + ~PAGE_MASK) & PAGE_MASK;
 	memset(page_address(page), 0, size);
 	*dma_addr = addr;
 	return page_address(page);
-- 
1.9.3

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