On Tue, 2015-05-12 at 09:28 +0200, Borislav Petkov wrote: > On Mon, May 11, 2015 at 04:09:39PM -0600, Toshi Kani wrote: > > There may not be any type conflict with MTRR_TYPE_INVALID. > > Because...? Because you cannot have a memory type conflict with MTRRs when MTRRs are disabled. mtrr_type_lookup() returns MTRR_TYPE_INVALID when MTRRs are disabled. This is stated in the comments of mtrr_type_lookup() and the MTRR_TYPE_INVALID definition itself. BIOS can disable MTRRs, or VM may choose not to implement MTRRs. The OS needs to handle this case as a valid config, and this is not an error case. > Let me guess: you cannot change this function to return a signed value > which is the type when positive and an error when negative? No, that is not the reason. > > I will change the caller to check MTRR_TYPE_INVALID, and treat it as a > > uniform case. > > That would be, of course, also wrong. I am confused... In your previous comments, you mentioned that: | If you want to be able to state that a type is uniform even if MTRRs | are disabled, you need to define another retval which means exactly | that. There may not be type conflict when MTRRs are disabled. There is no point of defining a new return value. | Or add an inline function called mtrr_enabled() and call it in the | mtrr_type_lookup() callers. MTRR_TYPE_INVALID means MTRRs disabled. So, the caller checking with this value is the same as checking with mtrr_enabled() you suggested. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>