Re: [PATCH v3 04/10] arm64/boot: Enable EL2 requirements for SPE_FEAT_FDS

[James Clark <james.clark@xxxxxxxxxx>]

On 14/07/2025 2:54 pm, Will Deacon wrote:
> On Thu, Jun 05, 2025 at 11:49:02AM +0100, James Clark wrote:
> > SPE data source filtering (optional from Armv8.8) requires that traps to
> > the filter register PMSDSFR be disabled. Document the requirements and
> > disable the traps if the feature is present.
> >
> > Tested-by: Leo Yan <leo.yan@xxxxxxx>
> > Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
> > ---
> >   Documentation/arch/arm64/booting.rst | 11 +++++++++++
> >   arch/arm64/include/asm/el2_setup.h   | 14 ++++++++++++++
> >   2 files changed, 25 insertions(+)
> >
> > diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst
> > index dee7b6de864f..abd75085a239 100644
> > --- a/Documentation/arch/arm64/booting.rst
> > +++ b/Documentation/arch/arm64/booting.rst
> > @@ -404,6 +404,17 @@ Before jumping into the kernel, the following conditions must be met:
> >       - HDFGWTR2_EL2.nPMICFILTR_EL0 (bit 3) must be initialised to 0b1.
> >       - HDFGWTR2_EL2.nPMUACR_EL1 (bit 4) must be initialised to 0b1.
> >   
> > +  For CPUs with SPE data source filtering (FEAT_SPE_FDS):
> > +
> > +  - If EL3 is present:
> > +
> > +    - MDCR_EL3.EnPMS3 (bit 42) must be initialised to 0b1.
> > +
> > +  - If the kernel is entered at EL1 and EL2 is present:
> > +
> > +    - HDFGRTR2_EL2.nPMSDSFR_EL1 (bit 19) must be initialised to 0b1.
> > +    - HDFGWTR2_EL2.nPMSDSFR_EL1 (bit 19) must be initialised to 0b1.
> > +
> >     For CPUs with Memory Copy and Memory Set instructions (FEAT_MOPS):
> >   
> >     - If the kernel is entered at EL1 and EL2 is present:
> > diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> > index 1e7c7475e43f..02b4a7fc016e 100644
> > --- a/arch/arm64/include/asm/el2_setup.h
> > +++ b/arch/arm64/include/asm/el2_setup.h
> > @@ -279,6 +279,20 @@
> >   	orr	x0, x0, #HDFGRTR2_EL2_nPMICFILTR_EL0
> >   	orr	x0, x0, #HDFGRTR2_EL2_nPMUACR_EL1
> >   .Lskip_pmuv3p9_\@:
> > +	mrs	x1, id_aa64dfr0_el1
> > +	ubfx	x1, x1, #ID_AA64DFR0_EL1_PMSVer_SHIFT, #4
> > +	/* If SPE is implemented, */
> > +	cmp	x1, #ID_AA64DFR0_EL1_PMSVer_IMP
> > +	b.lt	.Lskip_spefds_\@
> > +	/* we can read PMSIDR and */
> > +	mrs_s	x1, SYS_PMSIDR_EL1
> > +	and	x1, x1,  #PMSIDR_EL1_FDS
> > +	/* if FEAT_SPE_FDS is implemented, */
> > +	cbz	x1, .Lskip_spefds_\@
> > +	/* disable traps to PMSDSFR. */
> > +	orr	x0, x0, #HDFGRTR2_EL2_nPMSDSFR_EL1
>
> Why is this being done here rather than alongside the existing SPE
> configuration of HDFGRTR_EL2 and HDFGWTR_EL2 near the start of
> __init_el2_fgt?
>
> Will

I thought everything was separated by which trap configs it writes to, 
rather than the feature. This SPE feature is in HDFGRTR2 so I put it in 
__init_el2_fgt2 rather than __init_el2_fgt.

I suppose we could have a single __init_el2_spe that writes to both 
HDFGRTR and HDFGRTR2 but we'd have to be careful to not overwrite what 
was already done in the other sections.