[SeaBIOS] [PATCH v3] Update EFI_COMPATIBILITY16_TABLE to match 0.98 spec update

[David Woodhouse]

On Wed, 2014-05-28 at 09:58 -0400, Kevin O'Connor wrote:
> On Tue, May 20, 2014 at 02:22:16PM +0100, David Woodhouse wrote:
> > Unless CONFIG_MALLOC_UPPERMEMORY is turned off, we expect to use the
> > space between the top of option ROMs and the bottom of our own BIOS code
> > as a stack. OVMF was previously marking the whole region from 0xC0000 to
> > 0xFFFFF read-only before invoking our Legacy16Boot method. Read-only
> > stack considered harmful.
> > 
> > Version 0.98 of the CSM spec adds the UmaAddress and UmaSize fields, which
> > allow the CSM to specify a memory region that needs to be writable, so
> > provide that information.
> [...]
> > --- a/src/fw/csm.c
> > +++ b/src/fw/csm.c
> > @@ -34,6 +34,10 @@ EFI_COMPATIBILITY16_TABLE csm_compat_table VARFSEG __aligned(16) = {
> >      .Compatibility16CallOffset = 0 /* Filled in by checkrom.py */,
> >      .OemIdStringPointer = (u32)"SeaBIOS",
> >      .AcpiRsdPtrPointer = (u32)&csm_rsdp,
> > +#if CONFIG_MALLOC_UPPERMEMORY
> > +    .UmaAddress = (u32)&zonelow_base,
> > +    .UmaSize = 0x10000,
> > +#endif
> 
> Is there an advantage to setting this at compile time vs only setting
> these fields during runtime?

No, I don't believe so. We are invoked with *everything* writeable the
first time, so we don't have to have this filled in.

> > @@ -49,6 +53,11 @@ csm_return(struct bregs *regs)
> >      dprintf(3, "handle_csm returning AX=%04x\n", regs->ax);
> >  
> >      PICMask = pic_irqmask_read();
> > +    if (CONFIG_MALLOC_UPPERMEMORY) {
> > +        u32 top = rom_get_max();
> > +        csm_compat_table.UmaAddress = top;
> > +        csm_compat_table.UmaSize = (u32)zonelow_base + 0x10000 - top;
> > +    }
> 
> Would this work instead?
> 
>     u32 rommax = rom_get_max();
>     extern u8 final_readonly_start[];
>     csm_compat_table.UmaAddress = rommax;
>     csm_compat_table.UmaSize = (u32)final_readonly_start - rommax;
> 
> This should result in the same values as your patch when
> CONFIG_MALLOC_UPPERMEMORY.  For !CONFIG_MALLOC_UPPERMEMORY it will
> result in UmaAddress==final_readonly_start and UmaSize==0.

Looks sane; I'll test it. Perhaps when I get home next week.

-- 
dwmw2

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