Re: [PATCH 11/22] KVM: MMU: Add infrastructure for two-level page walker

Avi Kivity
2010-04-28T11:24:16Z

On 04/28/2010 01:52 PM, Joerg Roedel wrote:
> On Tue, Apr 27, 2010 at 03:34:10PM +0300, Avi Kivity wrote:
>
>> On 04/27/2010 01:38 PM, Joerg Roedel wrote:
>>
>>> This patch introduces a mmu-callback to translate gpa
>>> addresses in the walk_addr code. This is later used to
>>> translate l2_gpa addresses into l1_gpa addresses.
>>>
>>> +static inline gfn_t gpa_to_gfn(gpa_t gpa)
>>> +{
>>> + return (gfn_t)gpa>> PAGE_SHIFT;
>>> +}
>>> +
>>>
>> This overflows on 32-bit, since gpa_t is u64 and gfn_t is ulong.
>>
> Hm, this is a problem outside of this patchset too (for 32bit hosts).
> The best solution is probably to convert gfn_t to u64 too.
>

If you cast like

(gfn_t)(gpa >> PAGE_SHIFT)

you avoid the overflow for MAXPHYADDR < 48. However, I agree that
converting gfn_t to u64 is best, the minor performance degradation is in
no way comparable to the corruption that results from a miscast.

--
error compiling committee.c: too many arguments to function