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Re: [Xen-devel] [PATCH 03/14] xen/x86: Make mfn_to_gfn typesafe

On 10/05/2019 14:24, Jan Beulich wrote:
On 10.05.19 at 15:02, <julien.grall@xxxxxxx> wrote:

On 10/05/2019 12:35, Jan Beulich wrote:
On 07.05.19 at 17:14, <julien.grall@xxxxxxx> wrote:
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -474,7 +474,8 @@ static inline void trace_resync(int event, mfn_t gmfn)
       if ( tb_init_done )
           /* Convert gmfn to gfn */
-        unsigned long gfn = mfn_to_gfn(current->domain, gmfn);
+        unsigned long gfn = gfn_x(mfn_to_gfn(current->domain, gmfn));
           __trace_var(event, 0/*!tsc*/, sizeof(gfn), &gfn);

Can't you use gfn_t here, and hence avoid the gfn_x()? Same again further
Because __trace_var will export the value to the guest. I wasn't sure
whether we
can safely consider that gfn_t is exactly the same as unsigned long in

Hmm, well - see the definition of gfn_t. George, what do you think?

I know what's the current definition. My point is we never made that assumption before. In all honesty, sure assumption would definitely help in a few places, but I think we ought to safeguard with BUILD_BUG(...).


Julien Grall

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