[PATCH] xen/efi: Handle efi_memmap with Xen relocating itself

[Jason Andryuk <jason.andryuk@xxxxxxx>]

With Xen booting via Multiboot2/GRUB on an EFI platform, and modified to
use MULTIBOOT2_LOAD_PREFERENCE_LOW, Xen relocates itself with
move_xen().

However a PVH dom0 shows:
kernel: Failed to lookup header 0x77ffd000 in Xen memory map: error -3
kernel: ACPI=0x77ffd000

... for all the Xen efi memory map lookups.  Dumping the memory map at
runtime showed it was scrubbed.  Because Xen relocated itself, the
original physical address referenced through a directmap address goes
stale.

Add efi_arch_mmap_buffer_virt() to convert from the initial value to an
appropriate runtime value.  ARM uses Boot Services AllocatePool(), so it
must continue to use DIRECTMAP_VIRT_START.

For x86, we use an offset into the loaded Xen binary at the time of the
call and add the to XEN_VIRT_START.  ebmalloc() allocates from the Xen
image memory, so it moves during relocation.  xen_phys_start is set for
xen.efi in efi_exit_boot(), but not for xen.gz, so it cannot be used
Use `lea __image_base__(%rip)` to get the current load address, and use
that to calculate the offset into the Xen image.  That offset is also
valid from XEN_VIRT_START.

Fixes: c5b9805bc1f7 ("efi: create new early memory allocator")
Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
I think it could be seen without MULTIBOOT2_LOAD_PREFERENCE_LOW if xen
chose to relocate itself.  But since grub usually loads xen high, it
doesn't relocate itself.
---
 xen/arch/arm/efi/efi-boot.h |  5 +++++
 xen/arch/x86/efi/efi-boot.h | 10 ++++++++++
 xen/common/efi/boot.c       |  2 +-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
index 069cc68b0a..717bd8d607 100644
--- a/xen/arch/arm/efi/efi-boot.h
+++ b/xen/arch/arm/efi/efi-boot.h
@@ -449,6 +449,11 @@ static void *__init efi_arch_allocate_mmap_buffer(UINTN 
map_size)
     return ptr;
 }
 
+static void *__init efi_arch_mmap_buffer_virt(void *ptr)
+{
+    return ptr + DIRECTMAP_VIRT_START;
+}
+
 static void __init efi_arch_edd(void)
 {
 }
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index d738b839ee..ffc277ccfd 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -224,6 +224,16 @@ static void *__init efi_arch_allocate_mmap_buffer(UINTN 
map_size)
     return ebmalloc(map_size);
 }
 
+static void *__init efi_arch_mmap_buffer_virt(void *ptr)
+{
+    unsigned long load_base;
+
+    /* RIP-relative address is the current Xen load address. */
+    asm("lea __image_base__(%%rip), %0" : "=r" (load_base));
+
+    return ptr - load_base + XEN_VIRT_START;
+}
+
 static void __init efi_arch_pre_exit_boot(void)
 {
     if ( !trampoline_phys )
diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 89b5831691..5396bad7a5 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -1425,8 +1425,8 @@ static void __init efi_exit_boot(EFI_HANDLE ImageHandle, 
EFI_SYSTEM_TABLE *Syste
     /* Adjust pointers into EFI. */
     efi_ct = (const void *)efi_ct + DIRECTMAP_VIRT_START;
     efi_rs = (const void *)efi_rs + DIRECTMAP_VIRT_START;
-    efi_memmap = (void *)efi_memmap + DIRECTMAP_VIRT_START;
     efi_fw_vendor = (const void *)efi_fw_vendor + DIRECTMAP_VIRT_START;
+    efi_memmap = efi_arch_mmap_buffer_virt(efi_memmap);
 }
 
 /* SAF-1-safe */
-- 
2.34.1