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.