On Tue, 14 Feb, at 07:42:00PM, Sai Praneeth Prakhya wrote: > > It makes sense that "efi_sync_low_kernel_mappings()" would be the best > place but I added them here for these reasons > > 1. These mappings refer to "direct mapping of all physical memory" and > thus in "efi_map_regions()" we update *these* mappings to create 1:1 > mappings (to allow physical mode accesses by buggy firmware), so if we > copy these mappings in "efi_sync_low_kernel_mappings()" which is called > later than efi_map_regions(), we will overwrite previous 1:1 mappings > created by efi_map_regions() and hence kernel panics. > > 2. The other reason for adding these mappings in > "efi_alloc_page_tables()" is because that's the way mappings looked in > swapper_pgd before we shifted EFI stuff to efi_pgd. > > I have tested this by moving this code to > "efi_sync_low_kernel_mappings()" and I see that kernel panics in > set_virtual_address_map(). > > Please do correct me if you think otherwise. > > Thanks for the review, Matt OK, I now realise that I misunderstood this patch when I reviewed it the first time. Sorry about that. I see that the problem you're addressing is that some firmware will access the physical address of EFI_CONVENTIONAL_MEMORY regions while executing runtime services. And unless we're running in EFI mixed mode, we don't map EFI_CONVENTIONAL_MEMORY regions into the EFI page tables. We already have code to handle the 1:1 mapping of EFI_CONVENTIONAL_MEMORY because we need to do this for the EFI mixed mode scenario. The difference for non-mixed mode is that we only want to create the 1:1 mapping for EFI_CONVENTIONAL_MEMORY, we don't want the virtual mapping too. Lemme go and reply to your v2. -- 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
