Re: [PATCH v11 5/9] x86/efi: Disable LASS while mapping the EFI runtime services

Sohil Mehta
2025-10-31T19:04:15Z

On 10/31/2025 10:38 AM, Andy Lutomirski wrote:

> I have another question: why is this one specific call a problem as opposed to something more general? Wouldn’t any EFI call that touches the low EFI mapping be a problem? Are there any odd code paths that touch low mapped EFI *data* that would fault?
>

I assumed EFI is running in physical mode before this.
efi_sync_low_kernel_mappings() is called right before calling
set_virtual_address_map(). So, this is the only call that happens at the
low mapping while switching to virtual mode.

But, my EFI knowledge is fairly limited. I am realizing that there are
some assumptions built into this patch that I may not be aware of.

> Is there some way to be reasonably convinced that you haven’t missed another EFI code path?

We have been running the patches on internal test platforms for a couple
of years. But, that would only cover the common paths. I'll dig deeper
to get you a convincing answer.