Re: efi_enabled(EFI_PARAVIRT) use

[Ard Biesheuvel]

On 29 April 2016 at 16:39, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 29 Apr, at 11:34:45AM, Stefano Stabellini wrote:
>> On Fri, 29 Apr 2016, Ingo Molnar wrote:
>> > Also, it would be nice to have all things EFI in a single tree, the conflicts are
>> > going to be painful! There's very little reason not to carry this kind of commit:
>> >
>> >  arch/arm/xen/enlighten.c           |  6 +++++
>> >  drivers/firmware/efi/arm-runtime.c | 17 +++++++++-----
>> >  drivers/firmware/efi/efi.c         | 45 ++++++++++++++++++++++++++++++++------
>> >  3 files changed, 56 insertions(+), 12 deletions(-)
>> >
>> > in the EFI tree.
>>
>> That's true. I'll drop this commit from xentip and let Matt pick it up
>> or request changes as he sees fit.
>
> One small change I think would be sensible to make is to expand
> EFI_PARAVIRT into a few more bits to clearly indicate the quirks on
> Xen, and in the process, to delete EFI_PARAVIRT.
>
> That should address Ingo's major concern, and also make it much easier
> to rework the code in a piecemeal fashion.
>
> Could somebody enumerate the things that make Xen (dom0) different on
> arm* compared with bare metal EFI boot? The list I made for x86 was,
>
>   1. Has no EFI memory map
>   2. Runtime regions do not need to be mapped
>   3. Cannot call SetVirtualAddressMap()
>   4. /sys/firmware/efi/fw_vendor is invisible
>
> The first maps to not setting EFI_MEMMAP, the second to not setting
> EFI_RUNTIME. If we add EFI_ALREADY_VIRTUAL and EFI_FW_VENDOR_INVISIBLE
> to efi.flags that should cover everything on x86. Does arm* require
> anything else?

I already proposed when this patch was first under review to make the
arm_enable_runtime_services() function bail early without error if the
EFI_RUNTIME_SERVICES flag is already set, and the xen code could set
that bit as well when it installs its paravirtualized alternatives. I
don't remember exactly why that was shot down, though, but I think it
is the only reason this code introduces references to EFI_PARAVIRT in
the first place.