linux-kernel - RE: [PATCH] x86, pageattr: fix slow_virt_to_phys() for X86

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Date:	Wed, 29 Oct 2014 09:50:23 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"dave.hansen@...el.com" <dave.hansen@...el.com>,
	"riel@...hat.com" <riel@...hat.com>
CC:	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH] x86, pageattr: fix slow_virt_to_phys() for X86_PAE

> -----Original Message-----
> From: owner-linux-mm@...ck.org [mailto:owner-linux-mm@...ck.org] On
> Behalf Of Dexuan Cui
> Sent: Wednesday, October 29, 2014 18:54 PM
> To: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; linux-
> mm@...ck.org; x86@...nel.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.com; tglx@...utronix.de; mingo@...hat.com;
> hpa@...or.com; dave.hansen@...el.com; riel@...hat.com
> Cc: KY Srinivasan; Haiyang Zhang
> Subject: [PATCH] x86, pageattr: fix slow_virt_to_phys() for X86_PAE
> 
> pte_pfn() returns a PFN of long (32 bits in 32-PAE), then
> "long << PAGE_SHIFT" will overflow for PFNs above 4GB.
> 
> Due to this issue, some Linux 32-PAE distros, running as guests on Hyper-V,
> with 5GB memory assigned, can't load the netvsc driver successfully and
> hence the synthetic network device can't work (we can use the kernel
> parameter
> mem=3000M to work around the issue).
> 
> Cc: K. Y. Srinivasan <kys@...rosoft.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
>  arch/x86/mm/pageattr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index ae242a7..36de293 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -409,7 +409,7 @@ phys_addr_t slow_virt_to_phys(void *__virt_addr)
>  	psize = page_level_size(level);
>  	pmask = page_level_mask(level);
>  	offset = virt_addr & ~pmask;
> -	phys_addr = pte_pfn(*pte) << PAGE_SHIFT;
> +	phys_addr = (phys_addr_t)pte_pfn(*pte) << PAGE_SHIFT;
>  	return (phys_addr | offset);
>  }
>  EXPORT_SYMBOL_GPL(slow_virt_to_phys);

Sorry for sending the same patch twice due to my silly typing!

Thanks,
-- Dexuan
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