On Tue, Jul 15, 2025 at 02:28:19PM +0100, James Clark wrote: > > > On 15/07/2025 2:10 pm, James Clark wrote: > > > > > > On 15/07/2025 1:57 pm, Will Deacon wrote: > > > On Tue, Jul 15, 2025 at 01:48:03PM +0100, James Clark wrote: > > > > > > > > > > > > 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? > > > > > > > > > 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. > > > > > > That's fair; __init_el2_fgt isn't the right place. But the redundancy of > > > re-reading PMSVer from DFR0 is a little jarring. > > > > > > > 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. > > > > > > Right, perhaps it would be clearer to have trap-preserving macros for > > > features in a specific ID register rather than per-trap configuration > > > register macros. > > > > > > In other words, we have something like __init_fgt_aa64dfr0 which would > > > configure the FGT and FGT2 registers based on features in aa64dfr0. I > > > think you'd need to have a play to see how it ends up looking but the > > > main thing to avoid is having duplicate ID register parsing code for > > > setting up FGT and FGT2 traps. > > > > > > > I'll give it a go but that could end up being fragile to something that > > is dependent on two different ID registers in the future. Then we'd end > > up in the same situation for a different reason. > > > > I think I've run into it already. Wouldn't checking for FGT and FGT2 have to > be repeated when doing each ID register? Now we only do that once at the > start of __init_el2_fgt and __init_el2_fgt2, even if we might sometimes > check a different ID register twice. But if we flipped it we'd always have > to repeat those. Bah, this is quite horrible! Maybe the best we can do for now is have a macro for safely getting at PMBIDR? At some point, I suspect this whole FGT-configuration logic will need reworking but at the moment it's hard to see what the best approach would be. Will
