Re: [Xen-devel] [PATCH] Xen: ARM: Zero reserved fields of xatp before making hypervisor call

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jiandi,

Please respect the netiquette and wrap line to 70-75 characters.

On 20/12/2016 06:02, Jiandi An wrote:
> On 12/19/16 12:49, Stefano Stabellini wrote:
> > On Mon, 19 Dec 2016, Juergen Gross wrote:
> > > On 19/12/16 03:56, Jiandi An wrote:
> Thanks for you comments.  xatp is passed to XEN via the hypervisor call in each 
> loop.
> XEN touches xatp and returns it back.  For example XEN returns error of 
> underlying mapping call in the err[] array in xatp. (The err[] is not checked 
> after the hypervisor call returns and it's a bug to be addressed in a separate 
> patch)  XEN could theoretically corrupt xatp when it's returned.  And the loop 
> would go on to the next iteration passing in whatever that's in xatp returned 
> by the previous hypervisor call.  Harder to debug in my opinion if xatp get 
> corrupted by XEN somehow when a bug is introduced in XEN.  At first I put the 
> memset of xatp at the beginning outside of the loop.  But I thought it's better 
> to initialize xatp that's passed in each time a hypervisor call is made so we 
> know exactly we set going into the hypervisor call.
If you move struct xen_add_to_physmap_range in the loop, the compiler 
will initialize and zeroed for you the structure at each loop. I.e
for (i = 0; i < count; i++) {
        struct xen_add_to_physmap_range xapt = ....


}

Cheers,

--
Julien Grall

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