diff mbox

[v4,4/5] x86: add multiboot2 protocol support for EFI platforms

Message ID 0731e52830144d8c765e9d592e6855bd2b4e9869.1484748781.git-series.cardoe@cardoe.com (mailing list archive)
State New, archived
Headers show

Commit Message

Douglas Goldstein Jan. 18, 2017, 2:17 p.m. UTC
From: Daniel Kiper <daniel.kiper@oracle.com>

This way Xen can be loaded on EFI platforms using GRUB2 and
other boot loaders which support multiboot2 protocol.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>
Tested-by: Doug Goldstein <cardoe@cardoe.com>
---
Doug v2 - dropped all my changes and moved them into their own patch
Doug v1 - fix incorrect assembly (identified by Andrew Cooper)
   	- fix issue where the trampoline size was left as 0 and the
	  way the memory is allocated for the trampolines we would go to
	  the end of an available section and then subtract off the size
	  to decide where to place it. The end result was that we would
	  always copy the trampolines and the 32-bit stack into some
	  form of reserved memory after the conventional region we
	  wanted to put things into. On some systems this did not
	  manifest as a crash while on others it did. Reworked the
	  changes to always reserve 64kb for both the stack and the size
	  of the trampolines. Added an ASSERT to make sure we never blow
	  through this size.

v10 - suggestions/fixes:
    - replace ljmpl with lretq
      (suggested by Andrew Cooper),
    - introduce efi_platform to increase code readability
      (suggested by Andrew Cooper).

v9 - suggestions/fixes:
   - use .L labels instead of numeric ones in multiboot2 data scanning loops
     (suggested by Jan Beulich).

v8 - suggestions/fixes:
   - use __bss_start(%rip)/__bss_end(%rip) instead of
     of .startof.(.bss)(%rip)/$.sizeof.(.bss) because
     latter is not tested extensively in different
     built environments yet
     (suggested by Andrew Cooper),
   - fix multiboot2 data scanning loop in x86_32 code
     (suggested by Jan Beulich),
   - add check for extra mem for mbi data if Xen is loaded
     via multiboot2 protocol on EFI platform
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich).

v7 - suggestions/fixes:
   - do not allocate twice memory for trampoline if we were
     loaded via multiboot2 protocol on EFI platform,
   - wrap long line
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich).

v6 - suggestions/fixes:
   - improve label names in assembly
     error printing code
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich),
   - various minor cleanups and fixes
     (suggested by Jan Beulich).

v4 - suggestions/fixes:
   - remove redundant BSS alignment,
   - update BSS alignment check,
   - use __set_bit() instead of set_bit() if possible
     (suggested by Jan Beulich),
   - call efi_arch_cpu() from efi_multiboot2()
     even if the same work is done later in
     other place right now
     (suggested by Jan Beulich),
   - xen/arch/x86/efi/stub.c:efi_multiboot2()
     fail properly on EFI platforms,
   - do not read data beyond the end of multiboot2
     information in xen/arch/x86/boot/head.S
     (suggested by Jan Beulich),
   - use 32-bit registers in x86_64 code if possible
     (suggested by Jan Beulich),
   - multiboot2 information address is 64-bit
     in x86_64 code, so, treat it is as is
     (suggested by Jan Beulich),
   - use cmovcc if possible,
   - leave only one space between rep and stosq
     (suggested by Jan Beulich),
   - improve error handling,
   - improve early error messages,
     (suggested by Jan Beulich),
   - improve early error messages printing code,
   - improve label names
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich),
   - various minor cleanups.

v3 - suggestions/fixes:
   - take into account alignment when skipping multiboot2 fixed part
     (suggested by Konrad Rzeszutek Wilk),
   - improve segment registers initialization
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich and Konrad Rzeszutek Wilk),
   - improve commit message
     (suggested by Jan Beulich).

v2 - suggestions/fixes:
   - generate multiboot2 header using macros
     (suggested by Jan Beulich),
   - switch CPU to x86_32 mode before
     jumping to 32-bit code
     (suggested by Andrew Cooper),
   - reduce code changes to increase patch readability
     (suggested by Jan Beulich),
   - improve comments
     (suggested by Jan Beulich),
   - ignore MULTIBOOT2_TAG_TYPE_BASIC_MEMINFO tag on EFI platform
     and find on my own multiboot2.mem_lower value,
   - stop execution if EFI platform is detected
     in legacy BIOS path.
---
---
 xen/arch/x86/boot/head.S          | 263 +++++++++++++++++++++++++++++--
 xen/arch/x86/efi/efi-boot.h       |  54 +++++-
 xen/arch/x86/efi/stub.c           |  38 ++++-
 xen/arch/x86/x86_64/asm-offsets.c |   2 +-
 xen/arch/x86/xen.lds.S            |   4 +-
 xen/common/efi/boot.c             |  11 +-
 6 files changed, 349 insertions(+), 23 deletions(-)

Comments

Andrew Cooper Jan. 18, 2017, 7:51 p.m. UTC | #1
On 18/01/17 14:17, Doug Goldstein wrote:
> diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
> index d423fd8..ac93df0 100644
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -89,6 +89,13 @@ multiboot2_header_start:
>                     0, /* Number of the lines - no preference. */ \
>                     0  /* Number of bits per pixel - no preference. */
>  
> +        /* Inhibit bootloader from calling ExitBootServices(). */

/* Request that ExitBootServices() not be called. */

This tag doesn't make any guarantees.

> +        .code64
> +
> +__efi64_start:

__mb2_efi64_start:

This entry point is distinct from the PE efi64 entry point in
common/efi/boot.c

> +        cld
> +
> +        /* VGA is not available on EFI platforms. */
> +        movl   $0,vga_text_buffer(%rip)
> +
> +        /* Check for Multiboot2 bootloader. */
> +        cmp     $MULTIBOOT2_BOOTLOADER_MAGIC,%eax
> +        je      .Lefi_multiboot2_proto
> +
> +        /* Jump to not_multiboot after switching CPU to x86_32 mode. */
> +        lea     not_multiboot(%rip),%edi
> +        jmp     x86_32_switch
> +
> +.Lefi_multiboot2_proto:
> +        /* Zero EFI SystemTable and EFI ImageHandle addresses. */
> +        xor     %esi,%esi
> +        xor     %edi,%edi
> +
> +        /* Skip Multiboot2 information fixed part. */
> +        lea     (MB2_fixed_sizeof+MULTIBOOT2_TAG_ALIGN-1)(%rbx),%ecx
> +        and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx

Are we strictly guaranteed to have the entire image, including multiboot
tags, loaded below 4GB virtual even in the 64bit case? Even on non-EFI
capable grub2's ?

~Andrew
Douglas Goldstein Jan. 18, 2017, 8:05 p.m. UTC | #2
On 1/18/17 2:51 PM, Andrew Cooper wrote:
> On 18/01/17 14:17, Doug Goldstein wrote:
>> diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
>> index d423fd8..ac93df0 100644
>> --- a/xen/arch/x86/boot/head.S
>> +++ b/xen/arch/x86/boot/head.S
>> @@ -89,6 +89,13 @@ multiboot2_header_start:
>>                     0, /* Number of the lines - no preference. */ \
>>                     0  /* Number of bits per pixel - no preference. */
>>  
>> +        /* Inhibit bootloader from calling ExitBootServices(). */
> 
> /* Request that ExitBootServices() not be called. */
> 
> This tag doesn't make any guarantees.
>

Agreed. The multiboot2 spec is clear in that regard. I have tested the
case when the bootloader ignores this and it does work.

>> +        .code64
>> +
>> +__efi64_start:
> 
> __mb2_efi64_start:
> 
> This entry point is distinct from the PE efi64 entry point in
> common/efi/boot.c

I agree here as well. It does need one other update however. On line 97.

        /* EFI64 entry point. */
        mb2ht_init MB2_HT(ENTRY_ADDRESS_EFI64), MB2_HT(OPTIONAL), \
                   sym_phys(__efi64_start)

I can reroll the series or if people are comfortable with committing
this then the change can be done then.
Jan Beulich Jan. 19, 2017, 9:09 a.m. UTC | #3
>>> On 18.01.17 at 20:51, <andrew.cooper3@citrix.com> wrote:
> On 18/01/17 14:17, Doug Goldstein wrote:
>> +.Lefi_multiboot2_proto:
>> +        /* Zero EFI SystemTable and EFI ImageHandle addresses. */
>> +        xor     %esi,%esi
>> +        xor     %edi,%edi
>> +
>> +        /* Skip Multiboot2 information fixed part. */
>> +        lea     (MB2_fixed_sizeof+MULTIBOOT2_TAG_ALIGN-1)(%rbx),%ecx
>> +        and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx
> 
> Are we strictly guaranteed to have the entire image, including multiboot
> tags, loaded below 4GB virtual even in the 64bit case? Even on non-EFI
> capable grub2's ?

I can't speak for GrUB, but I've recently learned that EFI alone
doesn't appear to make such guarantees, and also doesn't look
to have ways to request such address restricted loading of an
image. Hence there'll be work needed to make at least xen.efi
cope with being loaded above that boundary.

Jan
Daniel Kiper Jan. 19, 2017, 11:37 a.m. UTC | #4
On Thu, Jan 19, 2017 at 02:09:37AM -0700, Jan Beulich wrote:
> >>> On 18.01.17 at 20:51, <andrew.cooper3@citrix.com> wrote:
> > On 18/01/17 14:17, Doug Goldstein wrote:
> >> +.Lefi_multiboot2_proto:
> >> +        /* Zero EFI SystemTable and EFI ImageHandle addresses. */
> >> +        xor     %esi,%esi
> >> +        xor     %edi,%edi
> >> +
> >> +        /* Skip Multiboot2 information fixed part. */
> >> +        lea     (MB2_fixed_sizeof+MULTIBOOT2_TAG_ALIGN-1)(%rbx),%ecx
> >> +        and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx
> >
> > Are we strictly guaranteed to have the entire image, including multiboot
> > tags, loaded below 4GB virtual even in the 64bit case? Even on non-EFI
> > capable grub2's ?
>
> I can't speak for GrUB, but I've recently learned that EFI alone

GRUB is able to enforce 4 GiB restriction. At least right now.
However, I am afraid that sooner or later machines will appear
in the wild which do not have memory below 4 GiB (well, they must
have some below 1 MiB but everything above is not a must as I know)
or everything will be reserved/used by EFI boot/runtime services, etc.
Then GRUB will also fail and we will be forced to extend multiboot2
proto further. However, it looks that current solution should not
change much then.

> doesn't appear to make such guarantees, and also doesn't look
> to have ways to request such address restricted loading of an

Why? Due to lack of memory below 4 GiB, it being reserved for
something, EFI implementation bugs or anything else?

Daniel
Jan Beulich Jan. 19, 2017, 12:03 p.m. UTC | #5
>>> On 19.01.17 at 12:37, <daniel.kiper@oracle.com> wrote:
> On Thu, Jan 19, 2017 at 02:09:37AM -0700, Jan Beulich wrote:
>> >>> On 18.01.17 at 20:51, <andrew.cooper3@citrix.com> wrote:
>> > Are we strictly guaranteed to have the entire image, including multiboot
>> > tags, loaded below 4GB virtual even in the 64bit case? Even on non-EFI
>> > capable grub2's ?
>>
>> I can't speak for GrUB, but I've recently learned that EFI alone
>> doesn't appear to make such guarantees, and also doesn't look
>> to have ways to request such address restricted loading of an
> 
> Why? Due to lack of memory below 4 GiB, it being reserved for
> something, EFI implementation bugs or anything else?

I don't know the precise reason in that specific case, but I did go
through the spec again after I had read that report, and I wasn't
able to find anything regarding mandated or optional address
restrictions. My recollection of there being such a restriction must
have been based on the EFI sample implementation and/or the
EDK.

Jan
diff mbox

Patch

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index d423fd8..ac93df0 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -89,6 +89,13 @@  multiboot2_header_start:
                    0, /* Number of the lines - no preference. */ \
                    0  /* Number of bits per pixel - no preference. */
 
+        /* Inhibit bootloader from calling ExitBootServices(). */
+        mb2ht_init MB2_HT(EFI_BS), MB2_HT(OPTIONAL)
+
+        /* EFI64 entry point. */
+        mb2ht_init MB2_HT(ENTRY_ADDRESS_EFI64), MB2_HT(OPTIONAL), \
+                   sym_phys(__efi64_start)
+
         /* Multiboot2 header end tag. */
         mb2ht_init MB2_HT(END), MB2_HT(REQUIRED)
 .Lmultiboot2_header_end:
@@ -100,20 +107,48 @@  multiboot2_header_start:
 gdt_boot_descr:
         .word   6*8-1
         .long   sym_phys(trampoline_gdt)
+        .long   0 /* Needed for 64-bit lgdt */
+
+        .align 4
+vga_text_buffer:
+        .long   0xb8000
+
+efi_platform:
+        .byte   0
 
 .Lbad_cpu_msg: .asciz "ERR: Not a 64-bit CPU!"
 .Lbad_ldr_msg: .asciz "ERR: Not a Multiboot bootloader!"
+.Lbad_ldr_nbs: .asciz "ERR: Bootloader shutdown EFI x64 boot services!"
+.Lbad_ldr_nst: .asciz "ERR: EFI SystemTable is not provided by bootloader!"
+.Lbad_ldr_nih: .asciz "ERR: EFI ImageHandle is not provided by bootloader!"
+.Lbad_efi_msg: .asciz "ERR: EFI IA-32 platforms are not supported!"
 
         .section .init.text, "ax", @progbits
 
 bad_cpu:
         mov     $(sym_phys(.Lbad_cpu_msg)),%esi # Error message
-        jmp     print_err
+        jmp     .Lget_vtb
 not_multiboot:
         mov     $(sym_phys(.Lbad_ldr_msg)),%esi # Error message
-print_err:
-        mov     $0xB8000,%edi  # VGA framebuffer
-1:      mov     (%esi),%bl
+        jmp     .Lget_vtb
+.Lmb2_no_st:
+        mov     $(sym_phys(.Lbad_ldr_nst)),%esi # Error message
+        jmp     .Lget_vtb
+.Lmb2_no_ih:
+        mov     $(sym_phys(.Lbad_ldr_nih)),%esi # Error message
+        jmp     .Lget_vtb
+.Lmb2_no_bs:
+        mov     $(sym_phys(.Lbad_ldr_nbs)),%esi # Error message
+        xor     %edi,%edi                       # No VGA text buffer
+        jmp     .Lsend_chr
+.Lmb2_efi_ia_32:
+        mov     $(sym_phys(.Lbad_efi_msg)),%esi # Error message
+        xor     %edi,%edi                       # No VGA text buffer
+        jmp     .Lsend_chr
+.Lget_vtb:
+        mov     sym_phys(vga_text_buffer),%edi
+.Lsend_chr:
+        mov     (%esi),%bl
         test    %bl,%bl        # Terminate on '\0' sentinel
         je      .Lhalt
         mov     $0x3f8+5,%dx   # UART Line Status Register
@@ -123,13 +158,186 @@  print_err:
         mov     $0x3f8+0,%dx   # UART Transmit Holding Register
         mov     %bl,%al
         out     %al,%dx        # Send a character over the serial line
-        movsb                  # Write a character to the VGA framebuffer
+        test    %edi,%edi      # Is the VGA text buffer available?
+        jz      .Lsend_chr
+        movsb                  # Write a character to the VGA text buffer
         mov     $7,%al
-        stosb                  # Write an attribute to the VGA framebuffer
-        jmp     1b
+        stosb                  # Write an attribute to the VGA text buffer
+        jmp     .Lsend_chr
 .Lhalt: hlt
         jmp     .Lhalt
 
+        .code64
+
+__efi64_start:
+        cld
+
+        /* VGA is not available on EFI platforms. */
+        movl   $0,vga_text_buffer(%rip)
+
+        /* Check for Multiboot2 bootloader. */
+        cmp     $MULTIBOOT2_BOOTLOADER_MAGIC,%eax
+        je      .Lefi_multiboot2_proto
+
+        /* Jump to not_multiboot after switching CPU to x86_32 mode. */
+        lea     not_multiboot(%rip),%edi
+        jmp     x86_32_switch
+
+.Lefi_multiboot2_proto:
+        /* Zero EFI SystemTable and EFI ImageHandle addresses. */
+        xor     %esi,%esi
+        xor     %edi,%edi
+
+        /* Skip Multiboot2 information fixed part. */
+        lea     (MB2_fixed_sizeof+MULTIBOOT2_TAG_ALIGN-1)(%rbx),%ecx
+        and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx
+
+.Lefi_mb2_tsize:
+        /* Check Multiboot2 information total size. */
+        mov     %ecx,%r8d
+        sub     %ebx,%r8d
+        cmp     %r8d,MB2_fixed_total_size(%rbx)
+        jbe     run_bs
+
+        /* Are EFI boot services available? */
+        cmpl    $MULTIBOOT2_TAG_TYPE_EFI_BS,MB2_tag_type(%rcx)
+        jne     .Lefi_mb2_st
+
+        /* We are on EFI platform and EFI boot services are available. */
+        incb    efi_platform(%rip)
+
+        /*
+         * Disable real mode and other legacy stuff which should not
+         * be run on EFI platforms.
+         */
+        incb    skip_realmode(%rip)
+        jmp     .Lefi_mb2_next_tag
+
+.Lefi_mb2_st:
+        /* Get EFI SystemTable address from Multiboot2 information. */
+        cmpl    $MULTIBOOT2_TAG_TYPE_EFI64,MB2_tag_type(%rcx)
+        cmove   MB2_efi64_st(%rcx),%rsi
+        je      .Lefi_mb2_next_tag
+
+        /* Get EFI ImageHandle address from Multiboot2 information. */
+        cmpl    $MULTIBOOT2_TAG_TYPE_EFI64_IH,MB2_tag_type(%rcx)
+        cmove   MB2_efi64_ih(%rcx),%rdi
+        je      .Lefi_mb2_next_tag
+
+        /* Is it the end of Multiboot2 information? */
+        cmpl    $MULTIBOOT2_TAG_TYPE_END,MB2_tag_type(%rcx)
+        je      run_bs
+
+.Lefi_mb2_next_tag:
+        /* Go to next Multiboot2 information tag. */
+        add     MB2_tag_size(%rcx),%ecx
+        add     $(MULTIBOOT2_TAG_ALIGN-1),%ecx
+        and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx
+        jmp     .Lefi_mb2_tsize
+
+run_bs:
+        /* Are EFI boot services available? */
+        cmpb    $0,efi_platform(%rip)
+        jnz     0f
+
+        /* Jump to .Lmb2_no_bs after switching CPU to x86_32 mode. */
+        lea     .Lmb2_no_bs(%rip),%edi
+        jmp     x86_32_switch
+
+0:
+        /* Is EFI SystemTable address provided by boot loader? */
+        test    %rsi,%rsi
+        jnz     1f
+
+        /* Jump to .Lmb2_no_st after switching CPU to x86_32 mode. */
+        lea     .Lmb2_no_st(%rip),%edi
+        jmp     x86_32_switch
+
+1:
+        /* Is EFI ImageHandle address provided by boot loader? */
+        test    %rdi,%rdi
+        jnz     2f
+
+        /* Jump to .Lmb2_no_ih after switching CPU to x86_32 mode. */
+        lea     .Lmb2_no_ih(%rip),%edi
+        jmp     x86_32_switch
+
+2:
+        push    %rax
+        push    %rdi
+
+        /*
+         * Initialize BSS (no nasty surprises!).
+         * It must be done earlier than in BIOS case
+         * because efi_multiboot2() touches it.
+         */
+        lea     __bss_start(%rip),%edi
+        lea     __bss_end(%rip),%ecx
+        sub     %edi,%ecx
+        shr     $3,%ecx
+        xor     %eax,%eax
+        rep stosq
+
+        pop     %rdi
+
+        /*
+         * efi_multiboot2() is called according to System V AMD64 ABI:
+         *   - IN: %rdi - EFI ImageHandle, %rsi - EFI SystemTable,
+         *   - OUT: %rax - highest usable memory address below 1 MiB;
+         *                 memory above this address is reserved for trampoline;
+         *                 memory below this address is used as a storage for
+         *                 mbi struct created in reloc().
+         *
+         * MULTIBOOT2_TAG_TYPE_BASIC_MEMINFO tag is not provided
+         * on EFI platforms. Hence, it could not be used like
+         * on legacy BIOS platforms.
+         */
+        call    efi_multiboot2
+
+        /* Convert memory address to bytes/16 and store it in safe place. */
+        shr     $4,%eax
+        mov     %eax,%ecx
+
+        pop     %rax
+
+        /* Jump to trampoline_setup after switching CPU to x86_32 mode. */
+        lea     trampoline_setup(%rip),%edi
+
+x86_32_switch:
+        cli
+
+        /* Initialize GDTR. */
+        lgdt    gdt_boot_descr(%rip)
+
+        /* Reload code selector. */
+        pushq   $BOOT_CS32
+        lea     cs32_switch(%rip),%edx
+        push    %rdx
+        lretq
+
+        .code32
+
+cs32_switch:
+        /* Initialize basic data segments. */
+        mov     $BOOT_DS,%edx
+        mov     %edx,%ds
+        mov     %edx,%es
+        mov     %edx,%ss
+        /* %esp is initialized later. */
+
+        /* Load null descriptor to unused segment registers. */
+        xor     %edx,%edx
+        mov     %edx,%fs
+        mov     %edx,%gs
+
+        /* Disable paging. */
+        mov     %cr0,%edx
+        and     $(~X86_CR0_PG),%edx
+        mov     %edx,%cr0
+
+        /* Jump to earlier loaded address. */
+        jmp     *%edi
+
 __start:
         cld
         cli
@@ -157,7 +365,7 @@  __start:
 
         /* Not available? BDA value will be fine. */
         cmovnz  MB_mem_lower(%ebx),%edx
-        jmp     trampoline_setup
+        jmp     trampoline_bios_setup
 
 .Lmultiboot2_proto:
         /* Skip Multiboot2 information fixed part. */
@@ -169,24 +377,33 @@  __start:
         mov     %ecx,%edi
         sub     %ebx,%edi
         cmp     %edi,MB2_fixed_total_size(%ebx)
-        jbe     trampoline_setup
+        jbe     trampoline_bios_setup
 
         /* Get mem_lower from Multiboot2 information. */
         cmpl    $MULTIBOOT2_TAG_TYPE_BASIC_MEMINFO,MB2_tag_type(%ecx)
         cmove   MB2_mem_lower(%ecx),%edx
-        je      trampoline_setup
+        je      .Lmb2_next_tag
+
+        /* EFI IA-32 platforms are not supported. */
+        cmpl    $MULTIBOOT2_TAG_TYPE_EFI32,MB2_tag_type(%ecx)
+        je      .Lmb2_efi_ia_32
+
+        /* Bootloader shutdown EFI x64 boot services. */
+        cmpl    $MULTIBOOT2_TAG_TYPE_EFI64,MB2_tag_type(%ecx)
+        je      .Lmb2_no_bs
 
         /* Is it the end of Multiboot2 information? */
         cmpl    $MULTIBOOT2_TAG_TYPE_END,MB2_tag_type(%ecx)
-        je      trampoline_setup
+        je      trampoline_bios_setup
 
+.Lmb2_next_tag:
         /* Go to next Multiboot2 information tag. */
         add     MB2_tag_size(%ecx),%ecx
         add     $(MULTIBOOT2_TAG_ALIGN-1),%ecx
         and     $~(MULTIBOOT2_TAG_ALIGN-1),%ecx
         jmp     .Lmb2_tsize
 
-trampoline_setup:
+trampoline_bios_setup:
         /* Set up trampoline segment 64k below EBDA */
         movzwl  0x40e,%ecx          /* EBDA segment */
         cmp     $0xa000,%ecx        /* sanity check (high) */
@@ -202,16 +419,19 @@  trampoline_setup:
          * multiboot structure (if available) and use the smallest.
          */
         cmp     $0x100,%edx         /* is the multiboot value too small? */
-        jb      2f                  /* if so, do not use it */
+        jb      trampoline_setup    /* if so, do not use it */
         shl     $10-4,%edx
         cmp     %ecx,%edx           /* compare with BDA value */
         cmovb   %edx,%ecx           /* and use the smaller */
 
-2:      /* Reserve 64kb for the trampoline */
+        /* Reserve 64kb for the trampoline. */
         sub     $0x1000,%ecx
 
         /* From arch/x86/smpboot.c: start_eip had better be page-aligned! */
         xor     %cl, %cl
+
+trampoline_setup:
+        /* Save trampoline address for later use. */
         shl     $4, %ecx
         mov     %ecx,sym_phys(trampoline_phys)
 
@@ -223,7 +443,14 @@  trampoline_setup:
         call    reloc
         mov     %eax,sym_phys(multiboot_ptr)
 
-        /* Initialize BSS (no nasty surprises!) */
+        /*
+         * Do not zero BSS on EFI platform here.
+         * It was initialized earlier.
+         */
+        cmpb    $0,sym_phys(efi_platform)
+        jnz     1f
+
+        /* Initialize BSS (no nasty surprises!). */
         mov     $sym_phys(__bss_start),%edi
         mov     $sym_phys(__bss_end),%ecx
         sub     %edi,%ecx
@@ -231,6 +458,7 @@  trampoline_setup:
         shr     $2,%ecx
         rep stosl
 
+1:
         /* Interrogate CPU extended features via CPUID. */
         mov     $0x80000000,%eax
         cpuid
@@ -282,8 +510,13 @@  trampoline_setup:
         cmp     $sym_phys(__trampoline_seg_stop),%edi
         jb      1b
 
+        /* Do not parse command line on EFI platform here. */
+        cmpb    $0,sym_phys(efi_platform)
+        jnz     1f
+
         call    cmdline_parse_early
 
+1:
         /* Switch to low-memory stack.  */
         mov     sym_phys(trampoline_phys),%edi
         lea     0x10000(%edi),%esp
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 62c010e..dc857d8 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -146,6 +146,8 @@  static void __init efi_arch_process_memory_map(EFI_SYSTEM_TABLE *SystemTable,
 {
     struct e820entry *e;
     unsigned int i;
+    /* Check for extra mem for mbi data if Xen is loaded via multiboot2 protocol. */
+    UINTN extra_mem = efi_enabled(EFI_LOADER) ? 0 : (64 << 10);
 
     /* Populate E820 table and check trampoline area availability. */
     e = e820map - 1;
@@ -168,7 +170,8 @@  static void __init efi_arch_process_memory_map(EFI_SYSTEM_TABLE *SystemTable,
             /* fall through */
         case EfiConventionalMemory:
             if ( !trampoline_phys && desc->PhysicalStart + len <= 0x100000 &&
-                 len >= cfg.size && desc->PhysicalStart + len > cfg.addr )
+                 len >= cfg.size + extra_mem &&
+                 desc->PhysicalStart + len > cfg.addr )
                 cfg.addr = (desc->PhysicalStart + len - cfg.size) & PAGE_MASK;
             /* fall through */
         case EfiLoaderCode:
@@ -210,12 +213,14 @@  static void *__init efi_arch_allocate_mmap_buffer(UINTN map_size)
 
 static void __init efi_arch_pre_exit_boot(void)
 {
-    if ( !trampoline_phys )
-    {
-        if ( !cfg.addr )
-            blexit(L"No memory for trampoline");
+    if ( trampoline_phys )
+        return;
+
+    if ( !cfg.addr )
+        blexit(L"No memory for trampoline");
+
+    if ( efi_enabled(EFI_LOADER) )
         relocate_trampoline(cfg.addr);
-    }
 }
 
 static void __init noreturn efi_arch_post_exit_boot(void)
@@ -653,6 +658,43 @@  static bool_t __init efi_arch_use_config_file(EFI_SYSTEM_TABLE *SystemTable)
 
 static void efi_arch_flush_dcache_area(const void *vaddr, UINTN size) { }
 
+paddr_t __init efi_multiboot2(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
+{
+    EFI_GRAPHICS_OUTPUT_PROTOCOL *gop;
+    UINTN cols, gop_mode = ~0, rows;
+
+    __set_bit(EFI_BOOT, &efi_flags);
+    __set_bit(EFI_RS, &efi_flags);
+
+    efi_init(ImageHandle, SystemTable);
+
+    efi_console_set_mode();
+
+    if ( StdOut->QueryMode(StdOut, StdOut->Mode->Mode,
+                           &cols, &rows) == EFI_SUCCESS )
+        efi_arch_console_init(cols, rows);
+
+    gop = efi_get_gop();
+
+    if ( gop )
+        gop_mode = efi_find_gop_mode(gop, 0, 0, 0);
+
+    efi_arch_edd();
+    efi_arch_cpu();
+
+    efi_tables();
+    setup_efi_pci();
+    efi_variables();
+
+    if ( gop )
+        efi_set_gop_mode(gop, gop_mode);
+
+    efi_exit_boot(ImageHandle, SystemTable);
+
+    /* Return highest usable memory address below 1 MiB. */
+    return cfg.addr;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/efi/stub.c b/xen/arch/x86/efi/stub.c
index 4158124..6ea6aa1 100644
--- a/xen/arch/x86/efi/stub.c
+++ b/xen/arch/x86/efi/stub.c
@@ -3,6 +3,44 @@ 
 #include <xen/init.h>
 #include <xen/lib.h>
 #include <asm/page.h>
+#include <asm/efibind.h>
+#include <efi/efidef.h>
+#include <efi/eficapsule.h>
+#include <efi/eficon.h>
+#include <efi/efidevp.h>
+#include <efi/efiapi.h>
+
+/*
+ * Here we are in EFI stub. EFI calls are not supported due to lack
+ * of relevant functionality in compiler and/or linker.
+ *
+ * efi_multiboot2() is an exception. Please look below for more details.
+ */
+
+paddr_t __init noreturn efi_multiboot2(EFI_HANDLE ImageHandle,
+                                       EFI_SYSTEM_TABLE *SystemTable)
+{
+    CHAR16 *err = L"Xen does not have EFI code build in!!!\r\nSystem halted!!!\r\n";
+    SIMPLE_TEXT_OUTPUT_INTERFACE *StdErr;
+
+    StdErr = SystemTable->StdErr ? SystemTable->StdErr : SystemTable->ConOut;
+
+    /*
+     * Print error message and halt the system.
+     *
+     * We have to open code MS x64 calling convention
+     * in assembly because here this convention may
+     * not be directly supported by C compiler.
+     */
+    asm volatile(
+    "    call %2                      \n"
+    "0:  hlt                          \n"
+    "    jmp  0b                      \n"
+       : "+c" (StdErr), "+d" (err) : "g" (StdErr->OutputString)
+       : "rax", "r8", "r9", "r10", "r11", "memory");
+
+    unreachable();
+}
 
 bool efi_enabled(unsigned int feature)
 {
diff --git a/xen/arch/x86/x86_64/asm-offsets.c b/xen/arch/x86/x86_64/asm-offsets.c
index 92f5d81..f135654 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -175,6 +175,8 @@  void __dummy__(void)
     OFFSET(MB2_tag_type, multiboot2_tag_t, type);
     OFFSET(MB2_tag_size, multiboot2_tag_t, size);
     OFFSET(MB2_mem_lower, multiboot2_tag_basic_meminfo_t, mem_lower);
+    OFFSET(MB2_efi64_st, multiboot2_tag_efi64_t, pointer);
+    OFFSET(MB2_efi64_ih, multiboot2_tag_efi64_ih_t, pointer);
     BLANK();
 
     OFFSET(DOMAIN_vm_assist, struct domain, vm_assist);
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index b0b1c9b..e0e2529 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -331,5 +331,5 @@  ASSERT(IS_ALIGNED(__init_end,   PAGE_SIZE), "__init_end misaligned")
 
 ASSERT(IS_ALIGNED(trampoline_start, 4), "trampoline_start misaligned")
 ASSERT(IS_ALIGNED(trampoline_end,   4), "trampoline_end misaligned")
-ASSERT(IS_ALIGNED(__bss_start,      4), "__bss_start misaligned")
-ASSERT(IS_ALIGNED(__bss_end,        4), "__bss_end misaligned")
+ASSERT(IS_ALIGNED(__bss_start,      8), "__bss_start misaligned")
+ASSERT(IS_ALIGNED(__bss_end,        8), "__bss_end misaligned")
diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 36dbb71..b6cbdad 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -79,6 +79,17 @@  static size_t wstrlen(const CHAR16 * s);
 static int set_color(u32 mask, int bpp, u8 *pos, u8 *sz);
 static bool_t match_guid(const EFI_GUID *guid1, const EFI_GUID *guid2);
 
+static void efi_init(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable);
+static void efi_console_set_mode(void);
+static EFI_GRAPHICS_OUTPUT_PROTOCOL *efi_get_gop(void);
+static UINTN efi_find_gop_mode(EFI_GRAPHICS_OUTPUT_PROTOCOL *gop,
+                               UINTN cols, UINTN rows, UINTN depth);
+static void efi_tables(void);
+static void setup_efi_pci(void);
+static void efi_variables(void);
+static void efi_set_gop_mode(EFI_GRAPHICS_OUTPUT_PROTOCOL *gop, UINTN gop_mode);
+static void efi_exit_boot(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable);
+
 static const EFI_BOOT_SERVICES *__initdata efi_bs;
 static UINT32 __initdata efi_bs_revision;
 static EFI_HANDLE __initdata efi_ih;