On Tue, 28 Feb, at 07:25:34PM, Sai Praneeth Prakhya wrote: > > > > > > > I don't think we should be adding yet another place in the EFI code > > > where we're modifying the page tables. > > > > > > We already have the ability to map EFI_CONVENTIONAL_MEMORY regions > > > inside of efi_map_regions() via the should_map_region() function. > > > > > > Currently, unless you're booting in mixed mode that function will > > > return 'false' if the region type is EFI_CONVENTIONAL_MEMORY, so to > > > get your machine booting you need to do two things, > > > > > > 1) Modify should_map_region() to allow EFI_CONVENTIONAL_MEMORY to be > > > mapped > > > > > > 2) Modify the 64-bit version of efi_map_region() to *only* create > > > 1:1 mapping for EFI_CONVENTIONAL_MEMORY regions. > > > > Thanks for the suggestions! Will try these and will let you know if that > > fixes the issue. > > > > I have noticed this issue on two machines HP laptop and a Desktop > (Gigabyte). Adding mappings for EFI_CONVENTIONAL_MEMORY and > *EFI_LOADER_DATA* solves the issue. Presently, I only have access to one > machine (Desktop) and as soon as I test this on laptop (hopefully it > does not access any other EFI regions illegally), I will send version 3 > of the patch. > > Since this patch will be mapping EFI_CONVENTIONAL_MEMORY and > EFI_LOADER_DATA in 1:1 mode on 64-bit machines, I think we could also do > the same with EFI_BOOT_SERVICES_DATA and EFI_BOOT_SERVICES_CODE. In > other words we could remove the existing mappings for > EFI_BOOT_SERVICES_CODE and EFI_BOOT_SERVICES_DATA from VA mapping. Do you know what data is being access in the EFI_LOADER_DATA region? Accessing that via the 1:1 mapping is really strange because the firmware will have had to convert any addresses the kernel gave it from virtual to physical (the kernel stores things in EFI_LOADER_DATA regions during boot). > I think; this should not break any machines because firmware could > access illegal addresses only in 1:1 mode and not in VA mode because > that's the only address space firmware has knowledge about. Firmware > doesn't know about virtual addresses until we pass them through > SetVirtualAddressMap(). > > So Matt, could you please confirm if you had come across any machines > that did illegal access to EFI regions using virtual addresses? I don't think I do have access to such machines, but what would removing the virtual mappings buy us? The risk of breaking machines with buggy firmware outweighs any benefit that I can think of. Am I missing something? -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
