Re: [Xen-devel] REGRESSION: Xen 4.13 RC5 fails to bootstrap Dom0 on ARM

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 19 Dec 2019, Julien Grall wrote:
> > > In fact most of people on Arm are using GRUB rather than EFI directly as
> > > this is more friendly to use.
> > > 
> > > Regarding the devicetree, Xen and Linux will completely ignore the
> > > memory nodes in Xen if using EFI. This because the EFI memory map will
> > > give you an overview of the platform with the EFI regions included.
> > 
> > Aha! So in that sense it is a bug in Xen after all, right? (that's what
> > you're
> > referring to when you say you now understand what needs to get fixed).
> 
> Yes. The EFI memory map is a list of existing memory with a type associated to
> it (Conventional, BootServiceCodes, MemoryMappedIO...).
> 
> The OS/Hypervisor will have to go through them and check which regions are
> usuable. Compare to Linux, Xen has limited itself to only a few types.
> 
> However, I think we can be on a par with Linux here.

I gave a look at the Linux implementation, the interesting bit is
drivers/firmware/efi/arm-init.c:is_usable_memory as far as I can tell.
I also gave a look at the Xen side, which is
xen/arch/arm/efi/efi-boot.h:efi_process_memory_map_bootinfo. As guessed,
the two are not quite the same.

One of the main differences is that Linux uses as "System RAM" even
regions that were marked as EFI_BOOT_SERVICES_CODE/DATA and
EFI_LOADER_CODE/DATA because they will get freed anyway. Xen doesn't
do that unless map_bs is set.

I wrote a quick patch to implement the Linux behavior on Xen, only
lightly tested. I can confirm that I see more memory this way. However,
I am not sure we actually want to import the Linux behavior wholesale.

Anyway, Roman, could you please let me know if this patch solves the
issue?



diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
index ca655ff003..ad18ff3669 100644
--- a/xen/arch/arm/efi/efi-boot.h
+++ b/xen/arch/arm/efi/efi-boot.h
@@ -149,10 +149,14 @@ static EFI_STATUS __init 
efi_process_memory_map_bootinfo(EFI_MEMORY_DESCRIPTOR *
 
     for ( Index = 0; Index < (mmap_size / desc_size); Index++ )
     {
-        if ( desc_ptr->Type == EfiConventionalMemory ||
-             (!map_bs &&
-              (desc_ptr->Type == EfiBootServicesCode ||
-               desc_ptr->Type == EfiBootServicesData)) )
+        if ( desc_ptr->Attribute == EFI_MEMORY_WB &&
+             (desc_ptr->Type == EfiConventionalMemory ||
+              desc_ptr->Type == EfiLoaderCode ||
+              desc_ptr->Type == EfiLoaderData ||
+              desc_ptr->Type == EfiACPIReclaimMemory ||
+              desc_ptr->Type == EfiPersistentMemory ||
+              desc_ptr->Type == EfiBootServicesCode ||
+              desc_ptr->Type == EfiBootServicesData) )
         {
             if ( !meminfo_add_bank(&bootinfo.mem, desc_ptr) )
             {
diff --git a/xen/include/efi/efidef.h b/xen/include/efi/efidef.h
index 86a7e111bf..f46207840f 100644
--- a/xen/include/efi/efidef.h
+++ b/xen/include/efi/efidef.h
@@ -147,6 +147,7 @@ typedef enum {
     EfiMemoryMappedIO,
     EfiMemoryMappedIOPortSpace,
     EfiPalCode,
+    EfiPersistentMemory,
     EfiMaxMemoryType
 } EFI_MEMORY_TYPE;
 

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