On Mon, Nov 26, 2018 at 06:50:09PM +0100, Ard Biesheuvel wrote:
> On Mon, 26 Nov 2018 at 18:46, Leif Lindholm <[email protected]> wrote:
> >
> > On Fri, Nov 23, 2018 at 01:14:28PM +0100, Ard Biesheuvel wrote:
> > > In preparation of permitting the virt code to define a larger PA space
> > > size via gEmbeddedTokenSpaceGuid.PcdPrePiCpuMemorySize than what the
> > > CPU actually supports, take the CPU's capabilities into account when
> > > setting up the page tables. This is necessary because KVM will shortly
> > > support variable PA space sizes, and to support running the same UEFI
> > > binaries regardless of that limit, PcdPrePiCpuMemorySize needs to be
> > > treated as an upper bound rather than a fixed size.
> >
> > Why do we keep PcdPrePiCpuMemorySize at all? (I.e., rather than just
> > using the probed value?
> > Mainly for the purpose of being able to restrict ourselves to 32/48
> > bits?
> >
> > If we keep it, should we rename
> > PcdPrePiCpuMemorySize -> PcdPrePiCpuMemoryBits
> > and
> > PcdPrePiCpuIoSize -> PcdPrePiCpuIoBits
> > ?
> >
> > Argument against this would be that later consumers still refer to
> > the value extracted from the HOB as SizeOf*Space, and happily shifts
> > 1s around by it :|
> >
>
> I am reworking this so PcdPrePiCpuMemorySize retains its meaning.
> Instead, I will add something like this to ArmLib.h
>
> //
> // ARM_MMU_IDMAP_LIMIT defines the maximum size of the identity mapping
> // that covers the entire address space when running in UEFI. This is limited
> // to what can architecturally be mapped using a 4 KB granule, even if the
> // hardware is capable of mapping more using larger pages.
> //
> #ifdef MDE_CPU_ARM
> #define ARM_MMU_IDMAP_LIMIT (MAX_UINT32)
> #else
> #define ARM_MMU_IDMAP_LIMIT (1ULL << 48)
> #endif
>
> and use that in the MMU code as an upper bound in case the CPU supports 52
> bits.
OK, that works for me.
And gets you off the hook for Pcd name bikesheding :)
/
Leif
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