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>>>> >>>>     asm volatile (".byte 0xf2, 0x0f, 0x01, 0xfc" >>>>                  : "=ccc" (res) >>>>                  : "a" (addr), "c" (fn)); >>>> >>>>     return res; >>>> } >>>> >>> The above constraints to use on_each_cpu_mask() is forcing the use of: >>> >>> void rmpopt(void *val) >> >> No.  You don't break your thin wrapper in order to force it into a >> wrong-shaped hole. >> >> You need something like this: >> >> void do_rmpopt_optimise(void *val) >> { >>     unsigned long addr = *(unsigned long *)val; >> >>     WARN_ON_ONCE(__rmpopt(addr, OPTIMISE)); >> } >> >> to invoke the wrapper safely from the IPI.  That will at obvious when >> something wrong occurs. > > This wrapper i can/will use, but doing a WARN_ON_ONCE() is probably avoidable as > there will be ranges where RMPOPT will always fail, such as while checking > the RMP table entries itself, so there is a good chance that we will always trigger > the WARN_ON_ONCE() on the memory range containing the RMP table. > To add, the above is in context of the current implementation, where we scan all memory up-to 2TB for applying RMP optimizations when SNP is enabled (and/or SNP_INIT). We will *always* get this stack trace during booting, so i think it makes sense to avoid this WARN_ON_ONCE(). Thanks, Ashish