Re: [Xen-devel] [PATCH v4 4/5] x86: add multiboot2 protocol support for EFI platforms
>>> On 19.01.17 at 12:37, wrote: > On Thu, Jan 19, 2017 at 02:09:37AM -0700, Jan Beulich wrote: >> >>> On 18.01.17 at 20:51, 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 ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v4 4/5] x86: add multiboot2 protocol support for EFI platforms
On Thu, Jan 19, 2017 at 02:09:37AM -0700, Jan Beulich wrote: > >>> On 18.01.17 at 20:51, 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 ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v4 4/5] x86: add multiboot2 protocol support for EFI platforms
>>> On 18.01.17 at 20:51, 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 ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v4 4/5] x86: add multiboot2 protocol support for EFI platforms
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. -- Doug Goldstein signature.asc Description: OpenPGP digital signature ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v4 4/5] x86: add multiboot2 protocol support for EFI platforms
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 ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
