Re: [PATCH v3] OvmfPkg/ResetVector: Depend on PCD values of the page tables.

["Marvin Häuser" <Marvin.Haeuser@outlook.com>]

Hey Laszlo,

I'm terribly sorry for the mistakes in v3, I made it in a hurry because it was late - should have postponded for today.
Because I didn't see 'your v3' (or didn't you post it yet?), I posted a v4 as you said, which should have fixed the three comments you had.

Thank you very much for your input!

Regards,
Marvin.

> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Friday, November 4, 2016 12:56 AM
> To: Marvin Häuser <Marvin.Haeuser@outlook.com>; edk2-
> devel@lists.01.org <edk2-devel@ml01.01.org>
> Cc: jordan.l.justen@intel.com
> Subject: Re: [PATCH v3] OvmfPkg/ResetVector: Depend on PCD values of the
> page tables.
> 
> Three comments:
> 
> On 11/03/16 22:41, Marvin Häuser wrote:
> > Currently, the value of the page tables' address is hard-coded in the
> > ResetVector. This patch replaces these values with a PCD dependency.
> >
> > A check for the size has been added to alert the developer to rewrite
> > the ASM according to the new size, if it has been changed.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.0
> > Signed-off-by: Marvin Haeuser <Marvin.Haeuser@outlook.com>
> > ---
> >  OvmfPkg/ResetVector/Ia32/PageTables64.asm | 23 ++++++++++----------
> >  OvmfPkg/ResetVector/ResetVector.inf       |  5 +++++
> >  OvmfPkg/ResetVector/ResetVector.nasmb     |  6 +++++
> >  3 files changed, 23 insertions(+), 11 deletions(-)
> >
> > diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > index b5a4cf8d7187..0b95a7fa9a86 100644
> > --- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > +++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > @@ -44,10 +44,11 @@ BITS    32
> >  SetCr3ForPageTables64:
> >
> >      ;
> > -    ; For OVMF, build some initial page tables at 0x800000-0x806000.
> > +    ; For OVMF, build some initial page tables at
> > +    ; PcdOvmfSecPageTablesBase - (PcdOvmfSecPageTablesBase + 0x6000).
> >      ;
> > -    ; This range should match with PcdOvmfSecPageTablesBase and
> > -    ; PcdOvmfSecPageTablesSize which are declared in the FDF files.
> > +    ; This range should match with PcdOvmfSecPageTablesSize which is
> > +    ; declared in the FDF files.
> >      ;
> >      ; At the end of PEI, the pages tables will be rebuilt into a
> >      ; more permanent location by DxeIpl.
> > @@ -56,21 +57,21 @@ SetCr3ForPageTables64:
> >      mov     ecx, 6 * 0x1000 / 4
> >      xor     eax, eax
> >  clearPageTablesMemoryLoop:
> > -    mov     dword[ecx * 4 + 0x800000 - 4], eax
> > +    mov     dword[ecx * 4 + PT_ADDR (0 - 4)], eax
> 
> I think this is incorrect (or dubious at least); the NASM-level replacement text
> for this will be
> 
>   (0x800000 + (0 - 4))
> 
> and I strongly dislike the (0 - 4) subexpression. The type in which NASM
> evaluates (0 - 4) is not specified, and I'd rather not risk it being UINT64, for
> example.
> 
> >      loop    clearPageTablesMemoryLoop
> >
> >      ;
> >      ; Top level Page Directory Pointers (1 * 512GB entry)
> >      ;
> > -    mov     dword[0x800000], 0x801000 + PAGE_PDP_ATTR
> > +    mov     dword[PT_ADDR (0)], PT_ADDR (0x1000) + PAGE_PDP_ATTR
> >
> >      ;
> >      ; Next level Page Directory Pointers (4 * 1GB entries => 4GB)
> >      ;
> > -    mov     dword[0x801000], 0x802000 + PAGE_PDP_ATTR
> > -    mov     dword[0x801008], 0x803000 + PAGE_PDP_ATTR
> > -    mov     dword[0x801010], 0x804000 + PAGE_PDP_ATTR
> > -    mov     dword[0x801018], 0x805000 + PAGE_PDP_ATTR
> > +    mov     dword[PT_ADDR (0x1000)], PT_ADDR (0x2000) +
> PAGE_PDP_ATTR
> > +    mov     dword[PT_ADDR (0x1008)], PT_ADDR (0x3000) +
> PAGE_PDP_ATTR
> > +    mov     dword[PT_ADDR (0x1010)], PT_ADDR (0x4000) +
> PAGE_PDP_ATTR
> > +    mov     dword[PT_ADDR (0x1018)], PT_ADDR (0x5000) +
> PAGE_PDP_ATTR
> >
> >      ;
> >      ; Page Table Entries (2048 * 2MB entries => 4GB) @@ -81,13 +82,13
> > @@ pageTableEntriesLoop:
> >      dec     eax
> >      shl     eax, 21
> >      add     eax, PAGE_2M_PDE_ATTR
> > -    mov     [ecx * 8 + 0x802000 - 8], eax
> > +    mov     [ecx * 8 + PT_ADDR (0x2000 - 8)], eax
> >      loop    pageTableEntriesLoop
> >
> >      ;
> >      ; Set CR3 now that the paging structures are available
> >      ;
> > -    mov     eax, 0x800000
> > +    mov     eax, PT_ADDR (0)
> >      mov     cr3, eax
> >
> >      OneTimeCallRet SetCr3ForPageTables64 diff --git
> > a/OvmfPkg/ResetVector/ResetVector.inf
> > b/OvmfPkg/ResetVector/ResetVector.inf
> > index 46610d243ecf..d1e5d4d9bdea 100644
> > --- a/OvmfPkg/ResetVector/ResetVector.inf
> > +++ b/OvmfPkg/ResetVector/ResetVector.inf
> > @@ -29,9 +29,14 @@ [Sources]
> >    ResetVector.nasmb
> >
> >  [Packages]
> > +  OvmfPkg/OvmfPkg.dec
> >    MdePkg/MdePkg.dec
> >    UefiCpuPkg/UefiCpuPkg.dec
> >
> >  [BuildOptions]
> >     *_*_IA32_NASMB_FLAGS = -
> I$(WORKSPACE)/UefiCpuPkg/ResetVector/Vtf0/
> >     *_*_X64_NASMB_FLAGS = -
> I$(WORKSPACE)/UefiCpuPkg/ResetVector/Vtf0/
> > +
> > +[Pcd]
> > +  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
> > +  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesSize
> > diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb
> > b/OvmfPkg/ResetVector/ResetVector.nasmb
> > index 31ac06ae4a8c..4bf8c97d8158 100644
> > --- a/OvmfPkg/ResetVector/ResetVector.nasmb
> > +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
> > @@ -53,6 +53,12 @@
> >  %include "Ia32/SearchForSecEntry.asm"
> >
> >  %ifdef ARCH_X64
> > +  %if (FixedPcdGet32 (PcdOvmfSecPageTablesSize) != 0x6000)
> > +    %error "This implementation inherently depends on
> PcdOvmfSecPageTablesSize"
> > +  %endif
> > +
> > +  #include <AutoGen.h>
> 
> I think this order is wrong. The C preprocessor won't fully expand
> FixedPcdGet32 (PcdOvmfSecPageTablesSize) I believe, because AutoGen.h
> is included after the use of the macro. In turn NASM won't find a plain
> numeric constant on the LHS of the inequality.
> 
> > +  %define PT_ADDR(Offset) FixedPcdGet32 (PcdOvmfSecPageTablesBase)
> 
> This misses the Offset macro param in the replacement text.
> 
> >  %include "Ia32/Flat32ToFlat64.asm"
> >  %include "Ia32/PageTables64.asm"
> >  %endif
> >
> 
> Marvin, please send a v4, or else please respond with your R-b to "my"
> v3 (and then we can commit that series, if Jordan agrees) -- either works for
> me.
> 
> Thanks
> Laszlo