Re: [RFC] ArmPkg/ArmMmuLib: Add new attribute WRITE_BACK_NONSHARE

[Leif Lindholm <leif.lindholm@linaro.org>]

On Tue, Nov 07, 2017 at 11:08:39AM +0000, Ard Biesheuvel wrote:
> On 7 November 2017 at 11:05, Heyi Guo <heyi.guo@linaro.org> wrote:
> > From: Peicong Li <lipeicong@huawei.com>
> >
> > Flash region needs to be set as cacheable (write back) to increase
> > performance, if PEI is still XIP on flash or DXE FV is decompressed
> > from flash FV. However some ARM platforms do not support to set flash
> > as inner shareable since flash is not normal DDR memory and it will
> > not respond to cache snoop request, which will causes system hang
> > after MMU is enabled.
> >
> > So we need a new ARM memory region attribute WRITE_BACK_NONSHARE for
> > flash region on these platforms specifically. This attribute will set
> > the region as write back but not inner shared.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Peicong Li <lipeicong@huawei.com>
> > Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
> > Cc: Leif Lindholm <leif.lindholm@linaro.org>
> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > ---
> >  ArmPkg/Include/Library/ArmLib.h                  | 2 ++
> >  ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 4 ++++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git a/ArmPkg/Include/Library/ArmLib.h b/ArmPkg/Include/Library/ArmLib.h
> > index 24ffe9f..e43e375 100644
> > --- a/ArmPkg/Include/Library/ArmLib.h
> > +++ b/ArmPkg/Include/Library/ArmLib.h
> > @@ -39,6 +39,8 @@
> >  typedef enum {
> >    ARM_MEMORY_REGION_ATTRIBUTE_UNCACHED_UNBUFFERED = 0,
> >    ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_UNCACHED_UNBUFFERED,
> > +  ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHARE,
> > +  ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK_NONSHARE,
> >    ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK,
> >    ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK,
> >    ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH,
> > diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> > index 8bd1c6f..cc10143 100644
> > --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> > +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> > @@ -35,6 +35,10 @@ ArmMemoryAttributeToPageAttribute (
> >    )
> >  {
> >    switch (Attributes) {
> > +  case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHARE:
> > +  case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK_NONSHARE:
> > +    return TT_ATTR_INDX_MEMORY_WRITE_BACK;
> > +
> >    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK:
> >    case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK:
> >      return TT_ATTR_INDX_MEMORY_WRITE_BACK | TT_SH_INNER_SHAREABLE;
> > --
> > 2.7.2.windows.1
> >
> 
> I'd prefer the name
> ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHAREABLE but other than
> that, this looks sensible to me. Leif?

And the same for NONSECURE, yes.
With that modification, this sounds like something absolutely required
in this situation.

Does this scenario have any further implications for runtime use?

/
    Leif