Re: [PATCH] Update qemu-kvm to allow a larger BIOS image.

[Sheng Yang <sheng@linux.intel.com>]

On Thursday 16 July 2009 12:57:02 Jordan Justen wrote:
> On Wed, Jul 15, 2009 at 8:08 PM, Sheng Yang<sheng@linux.intel.com> wrote:
> > On Thursday 16 July 2009 10:58:53 Jordan Justen wrote:
> >> On Wed, Jul 15, 2009 at 6:34 PM, Sheng Yang <sheng@linux.intel.com> 
wrote:
> >> > On Thursday 16 July 2009 08:12:15 Jordan Justen wrote:
> >> > > Motivation for making these changes:
> >> > >
> >> > > A larger firmware image size allows alternative BIOS images to be
> >> > > used with KVM.  Some possible uses are to enable UEFI firmware
> >> > > or coreboot firmware.  Additionally, an alternative firmware might
> >> > > include a linux kernel+initrd payload, which would require several
> >> > > megabytes.
> >> >
> >> > I think if you update bios to UEFI, the E820 should be represented by
> >> > UEFI rather than current bios?
> >>
> >> Yeah, that is true.  But, that firmware would be separate from the
> >> qemu-kvm tree at this time, right?
> >
> > Yes, so currently from QEmu-kvm side, I think it may not necessary to
> > update, for the patches haven't followed up yet...
>
> Of the two patches (1. kvm kernel module, 2. qemu-kvm), I think it
> is best if the qemu-kvm change happens first.  Since the qemu-kvm
> patch will cause the qemu-kvm bios to add more memory regions
> as reserved, the new change to qemu-kvm will be compatible with
> both the old and new versions of the kvm kernel module.
>
> >> But, in this patch it is critical that the 'VMX TSS Pages' are moved
> >> within qemu-kvm so the conflict with the larger bios.bin is removed.
> >
> > Well, for we are using a small size bios now, and larger bios would be
> > totally another story, I don't think push the modification now to the
> > upstream make sense. These modification can go with further patches with
> > UEFI at any time in the future.
>
> I am working on this UEFI firmware project which currently supports QEMU:
> https://edk2.tianocore.org/OVMF.html
>
> I would like it to also support KVM, and I found that it can already boot
> the UEFI shell on KVM if these two patches are applied.
>
> If these patches make some progress, I will update OVMF to reserve the
> appropriate memory regions.

Make sense to me. So what's mattered here is not bios, but qemu-kvm and kvm 
code. The user can replace bios binary by UEFI binary easily, but not with kvm 
related part.

I realized you still need separate the qemu-kvm patch into two: one for bios 
and another for qemu. And I just hope this modification won't break some old 
OS(any OS got assumption about bios size? I think Tiano team should have idea 
on it)...

-- 
regards
Yang, Sheng

>
> > --
> > regards
> > Yang, Sheng
> >
> >> > --
> >> > regards
> >> > Yang, Sheng
> >> >
> >> > > Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
> >> > > ---
> >> > >  kvm/bios/rombios.c        |    8 ++++----
> >> > >  kvm/include/x86/asm/vmx.h |    2 +-
> >> > >  qemu-kvm-x86.c            |    2 +-
> >> > >  3 files changed, 6 insertions(+), 6 deletions(-)
> >> > >
> >> > > diff --git a/kvm/bios/rombios.c b/kvm/bios/rombios.c
> >> > > index 6186199..2d0c153 100644
> >> > > --- a/kvm/bios/rombios.c
> >> > > +++ b/kvm/bios/rombios.c
> >> > > @@ -4596,14 +4596,14 @@ ASM_END
> >> > >                      case 5:
> >> > >                          /* 4 pages before the bios, 3 pages for vmx
> >> > > tss pages, * the other page for EPT real mode pagetable */
> >> > > -                        set_e820_range(ES, regs.u.r16.di,
> >> > > 0xfffbc000L, -                                       0xfffc0000L, 0,
> >> > > 0, 2); +                        set_e820_range(ES, regs.u.r16.di,
> >> > > 0xfeffc000L, +                                       0xff000000L, 0,
> >> > > 0, 2); regs.u.r32.ebx = 6;
> >> > >                          break;
> >> > >                      case 6:
> >> > > -                        /* 256KB BIOS area at the end of 4 GB */
> >> > > +                        /* 16MB BIOS area at the end of 4 GB */
> >> > >                          set_e820_range(ES, regs.u.r16.di,
> >> > > -                                       0xfffc0000L, 0x00000000L ,0,
> >> > > 0, 2); +                                       0xff000000L,
> >> > > 0x00000000L ,0, 0, 2); if (extra_highbits_memory_size ||
> >> > > extra_lowbits_memory_size) regs.u.r32.ebx = 7;
> >> > >                          else
> >> > > diff --git a/kvm/include/x86/asm/vmx.h b/kvm/include/x86/asm/vmx.h
> >> > > index df8d4f9..99e2bb9 100644
> >> > > --- a/kvm/include/x86/asm/vmx.h
> >> > > +++ b/kvm/include/x86/asm/vmx.h
> >> > > @@ -403,7 +403,7 @@ enum vmcs_field {
> >> > >  #define VMX_EPT_EXECUTABLE_MASK                      0x4ull
> >> > >  #define VMX_EPT_IGMT_BIT                     (1ull << 6)
> >> > >
> >> > > -#define VMX_EPT_IDENTITY_PAGETABLE_ADDR              0xfffbc000ul
> >> > > +#define VMX_EPT_IDENTITY_PAGETABLE_ADDR              0xfeffc000ul
> >> > >
> >> > >
> >> > >  #define ASM_VMX_VMCLEAR_RAX       ".byte 0x66, 0x0f, 0xc7, 0x30"
> >> > > diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
> >> > > index daf60b6..b5306aa 100644
> >> > > --- a/qemu-kvm-x86.c
> >> > > +++ b/qemu-kvm-x86.c
> >> > > @@ -63,7 +63,7 @@ static int kvm_init_tss(kvm_context_t kvm)
> >> > >                * this address is 3 pages before the bios, and the
> >> > > bios should present * as unavaible memory
> >> > >                */
> >> > > -             r = kvm_set_tss_addr(kvm, 0xfffbd000);
> >> > > +             r = kvm_set_tss_addr(kvm, 0xfeffd000);
> >> > >               if (r < 0) {
> >> > >                       fprintf(stderr, "kvm_init_tss: unable to set
> >> > > tss addr\n"); return r;
> >> >
> >> > --
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