RE: [PATCH] x86, pageattr: fix slow_virt_to_phys() for X86_PAE

[Dexuan Cui <decui@microsoft.com>]

> -----Original Message-----
> From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On
> Behalf Of Dexuan Cui
> Sent: Wednesday, October 29, 2014 18:54 PM
> To: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; x86@kernel.org; olaf@aepfle.de; apw@canonical.com;
> jasowang@redhat.com; tglx@linutronix.de; mingo@redhat.com;
> hpa@zytor.com; dave.hansen@intel.com; riel@redhat.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@microsoft.com>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Signed-off-by: Dexuan Cui <decui@microsoft.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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