On Sat, Oct 21, 2023 at 02:33:47AM +0100, Andrew Cooper wrote: > On 21/10/2023 2:18 am, Pawan Gupta wrote: > > On Sat, Oct 21, 2023 at 12:55:45AM +0100, Andrew Cooper wrote: > >> Also it avoids playing games with hiding data inside an instruction. > >> It's a neat trick, but the neater trick is avoid it whenever possible. > > Thanks for the pointers. I think verw in 32-bit mode won't be able to > > address the operand outside of 4GB range. > > And? In a 32bit kernel, what lives outside of a 4G range? > > > Maybe this is fine or could it > > be a problem addressing from e.g. KVM module? > > RIP-relative addressing is disp32. Which is the same as it is for > direct calls. > > So if your module is far enough away for VERW to have issues, you've got > far more basic problems to solve first. Sorry, I raised the wrong problem. In 64-bit mode, verww only has 32-bit of relative addressing, so memory operand has to be within 4GB of callsite. That could be a constraint.
