On 5/29/24 16:21, Mark Rutland wrote: > On Fri, Apr 05, 2024 at 08:16:34AM +0530, Anshuman Khandual wrote: >> Fine grained trap control for BRBE registers, and instructions access need >> to be configured in HDFGRTR_EL2, HDFGWTR_EL2 and HFGITR_EL2 registers when >> kernel enters at EL1 but EL2 is present. This changes __init_el2_fgt() as >> required. >> >> Similarly cycle and mis-prediction capture need to be enabled in BRBCR_EL1 >> and BRBCR_EL2 when the kernel enters either into EL1 or EL2. This adds new >> __init_el2_brbe() to achieve this objective. >> >> This also updates Documentation/arch/arm64/booting.rst with all the above >> EL2 along with MDRC_EL3.SBRBE requirements. >> >> First this replaces an existing hard encoding (1 << 62) with corresponding >> applicable macro HDFGRTR_EL2_nPMSNEVFR_EL1_MASK. >> >> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> >> Cc: Will Deacon <will@xxxxxxxxxx> >> Cc: Jonathan Corbet <corbet@xxxxxxx> >> Cc: Marc Zyngier <maz@xxxxxxxxxx> >> Cc: Oliver Upton <oliver.upton@xxxxxxxxx> >> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >> Cc: linux-doc@xxxxxxxxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx >> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> >> ---- >> Changes in V17: >> >> - New patch added in the series >> - Separated out from the BRBE driver implementation patch >> - Dropped the comment in __init_el2_brbe() >> - Updated __init_el2_brbe() with BRBCR_EL2.MPRED requirements >> - Updated __init_el2_brbe() with __check_hvhe() constructs >> - Updated booting.rst regarding MPRED, MDCR_EL3 and fine grained control >> >> Documentation/arch/arm64/booting.rst | 26 ++++++++ >> arch/arm64/include/asm/el2_setup.h | 90 +++++++++++++++++++++++++++- >> 2 files changed, 113 insertions(+), 3 deletions(-) >> >> diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst >> index b57776a68f15..512210da7dd2 100644 >> --- a/Documentation/arch/arm64/booting.rst >> +++ b/Documentation/arch/arm64/booting.rst >> @@ -349,6 +349,32 @@ Before jumping into the kernel, the following conditions must be met: >> >> - HWFGWTR_EL2.nSMPRI_EL1 (bit 54) must be initialised to 0b01. >> >> + For CPUs with feature Branch Record Buffer Extension (FEAT_BRBE): >> + >> + - If the kernel is entered at EL2 and EL1 is present: >> + >> + - BRBCR_EL1.CC (bit 3) must be initialised to 0b1. >> + - BRBCR_EL1.MPRED (bit 4) must be initialised to 0b1. > > IIUC this isn't necessary; if the kernel is entered at EL2, it's capable > of initializing the EL1 regs, and it doesn't look like this silently > affects something we'd need in the absence of a BRBE driver. No, this does not affect anything other than the BRBE driver. > > AFAICT the __init_el2_brbe() code you add below handles this, so I think > this is redundant and can be deleted. Did not understand the above. __init_el2_brbe() handles setting both BRBCR_EL2 and BRBCR_EL1 for CC and MPRED config irrespective of whether the kernel enters EL2 directly or enters EL1 via EL2. But should not that be documented here for both those scenarios ? OR because once the kernel is in EL2, it can configure EL1 as required, so it is not a booting requirement anymore ? > >> + - If the kernel is entered at EL1 and EL2 is present: >> + >> + - BRBCR_EL2.CC (bit 3) must be initialised to 0b1. >> + - BRBCR_EL2.MPRED (bit 4) must be initialised to 0b1. >> + >> + - HDFGRTR_EL2.nBRBDATA (bit 61) must be initialised to 0b1. >> + - HDFGRTR_EL2.nBRBCTL (bit 60) must be initialised to 0b1. >> + - HDFGRTR_EL2.nBRBIDR (bit 59) must be initialised to 0b1. >> + >> + - HDFGWTR_EL2.nBRBDATA (bit 61) must be initialised to 0b1. >> + - HDFGWTR_EL2.nBRBCTL (bit 60) must be initialised to 0b1. >> + >> + - HFGITR_EL2.nBRBIALL (bit 56) must be initialised to 0b1. >> + - HFGITR_EL2.nBRBINJ (bit 55) must be initialised to 0b1. >> + >> + - If EL3 is present: >> + >> + - MDCR_EL3.SBRBE (bits 33:32) must be initialised to 0b11. > > Minor nit: please list the EL3 requirements first, that way this can be > read in EL3->EL2->EL1 order to match the FW boot-flow order. Makes sense, will change the order. > >> + >> For CPUs with the Scalable Matrix Extension FA64 feature (FEAT_SME_FA64): >> >> - If EL3 is present: >> diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h >> index b7afaa026842..7c12a8e658d4 100644 >> --- a/arch/arm64/include/asm/el2_setup.h >> +++ b/arch/arm64/include/asm/el2_setup.h >> @@ -154,6 +154,41 @@ >> .Lskip_set_cptr_\@: >> .endm >> >> +#ifdef CONFIG_ARM64_BRBE >> +/* >> + * Enable BRBE cycle count and miss-prediction >> + * >> + * BRBE requires both BRBCR_EL1.CC and BRBCR_EL2.CC fields, be set >> + * for the cycle counts to be available in BRBINF<N>_EL1.CC during >> + * branch record processing after a PMU interrupt. This enables CC >> + * field on both these registers while still executing inside EL2. > > Huh, it's a bit of an oddity to do that for a register that gets the E2H > treatment, but that is what the ARM ARM says, looking at the pseudocode > in ARM DDI 0487K.a: > > | // BRBCycleCountingEnabled() > | // ========================= > | // Returns TRUE if the recording of cycle counts is allowed, > | // FALSE otherwise. > | boolean BRBCycleCountingEnabled() > | if HaveEL(EL2) && BRBCR_EL2.CC == '0' then return FALSE; > | if BRBCR_EL1.CC == '0' then return FALSE; > | return TRUE; > > ... and likewise for MPRED: > > | // BRBEMispredictAllowed() > | // ======================= > | // Returns TRUE if the recording of branch misprediction is allowed, > | // FALSE otherwise. > | boolean BRBEMispredictAllowed() > | if HaveEL(EL2) && BRBCR_EL2.MPRED == '0' then return FALSE; > | if BRBCR_EL1.MPRED == '0' then return FALSE; > | return TRUE; > > ... though BRBCycleCountingEnabled() isn't actually used anywhere, while > BRBEMispredictAllowed is used by BRBEBranch(), since that does: > > | (ccu, cc) = BranchEncCycleCount(); > | ... > | bit mispredict = if BRBEMispredictAllowed() && BranchMispredict() then '1' else '0'; > > ... where BranchEncCycleCount() is a stub that doesn't mention > BRBCycleCountingEnabled() at all, so it's not clear to me whether CCU is > guaranteed to be set. > >> + * >> + * BRBE driver would still be able to toggle branch records cycle >> + * count support via BRBCR_EL1.CC field regardless of whether the >> + * kernel ends up executing in EL1 or EL2. >> + * >> + * The same principle applies for branch record mis-prediction info >> + * as well, thus requiring MPRED field to be set on both BRBCR_EL1 >> + * and BRBCR_EL2 while still executing inside EL2. >> + */ > > I think we can clarify this comment to: > > /* > * Enable BRBE to record cycle counts and branch mispredicts. > * > * At any EL, to record cycle counts BRBE requires that both > * BRBCR_EL2.CC=1 and BRBCR_EL1.CC=1. > * > * At any EL, to record branch mispredicts BRBE requires that both > * BRBCR_EL2.MPRED=1 and BRBCR_EL1.MPRED=1. > * > * When HCR_EL2.E2H=1, the BRBCR_EL1 encoding is redirected to > * BRBCR_EL2, but the {CC,MPRED} bits in the real BRBCR_EL1 register > * still apply. > * > * Set {CC,MPRBED} in both BRBCR_EL2 and BRBCR_EL1 so that at runtime we > * only need to enable/disable thse in BRBCR_EL1 regardless of whether > * the kernel ends up executing in EL1 or EL2. > */ Sure, will update this comment. > >> +.macro __init_el2_brbe >> + mrs x1, id_aa64dfr0_el1 >> + ubfx x1, x1, #ID_AA64DFR0_EL1_BRBE_SHIFT, #4 >> + cbz x1, .Lskip_brbe_\@ >> + >> + mov_q x0, BRBCR_ELx_CC | BRBCR_ELx_MPRED >> + msr_s SYS_BRBCR_EL2, x0 >> + >> + __check_hvhe .Lset_brbe_nvhe_\@, x1 >> + msr_s SYS_BRBCR_EL12, x0 // VHE >> + b .Lskip_brbe_\@ >> + >> +.Lset_brbe_nvhe_\@: >> + msr_s SYS_BRBCR_EL1, x0 // NVHE >> +.Lskip_brbe_\@: >> +.endm >> +#endif /* CONFIG_ARM64_BRBE */ >> + >> /* Disable any fine grained traps */ >> .macro __init_el2_fgt >> mrs x1, id_aa64mmfr0_el1 >> @@ -161,16 +196,48 @@ >> cbz x1, .Lskip_fgt_\@ >> >> mov x0, xzr >> + mov x2, xzr >> mrs x1, id_aa64dfr0_el1 >> ubfx x1, x1, #ID_AA64DFR0_EL1_PMSVer_SHIFT, #4 >> cmp x1, #3 >> b.lt .Lset_debug_fgt_\@ >> + >> /* Disable PMSNEVFR_EL1 read and write traps */ >> - orr x0, x0, #(1 << 62) >> + orr x0, x0, #HDFGRTR_EL2_nPMSNEVFR_EL1_MASK >> + orr x2, x2, #HDFGWTR_EL2_nPMSNEVFR_EL1_MASK >> >> .Lset_debug_fgt_\@: >> +#ifdef CONFIG_ARM64_BRBE >> + mrs x1, id_aa64dfr0_el1 >> + ubfx x1, x1, #ID_AA64DFR0_EL1_BRBE_SHIFT, #4 >> + cbz x1, .Lskip_brbe_reg_fgt_\@ >> + >> + /* >> + * Disable read traps for the following registers >> + * >> + * [BRBSRC|BRBTGT|RBINF]_EL1 >> + * [BRBSRCINJ|BRBTGTINJ|BRBINFINJ|BRBTS]_EL1 >> + */ >> + orr x0, x0, #HDFGRTR_EL2_nBRBDATA_MASK >> + >> + /* >> + * Disable write traps for the following registers >> + * >> + * [BRBSRCINJ|BRBTGTINJ|BRBINFINJ|BRBTS]_EL1 >> + */ >> + orr x2, x2, #HDFGWTR_EL2_nBRBDATA_MASK >> + >> + /* Disable read and write traps for [BRBCR|BRBFCR]_EL1 */ >> + orr x0, x0, #HDFGRTR_EL2_nBRBCTL_MASK >> + orr x2, x2, #HDFGWTR_EL2_nBRBCTL_MASK >> + >> + /* Disable read traps for BRBIDR_EL1 */ >> + orr x0, x0, #HDFGRTR_EL2_nBRBIDR_MASK >> + >> +.Lskip_brbe_reg_fgt_\@: >> +#endif /* CONFIG_ARM64_BRBE */ >> msr_s SYS_HDFGRTR_EL2, x0 >> - msr_s SYS_HDFGWTR_EL2, x0 >> + msr_s SYS_HDFGWTR_EL2, x2 >> >> mov x0, xzr >> mrs x1, id_aa64pfr1_el1 >> @@ -193,7 +260,21 @@ >> .Lset_fgt_\@: >> msr_s SYS_HFGRTR_EL2, x0 >> msr_s SYS_HFGWTR_EL2, x0 >> - msr_s SYS_HFGITR_EL2, xzr >> + mov x0, xzr >> +#ifdef CONFIG_ARM64_BRBE >> + mrs x1, id_aa64dfr0_el1 >> + ubfx x1, x1, #ID_AA64DFR0_EL1_BRBE_SHIFT, #4 >> + cbz x1, .Lskip_brbe_insn_fgt_\@ >> + >> + /* Disable traps for BRBIALL instruction */ >> + orr x0, x0, #HFGITR_EL2_nBRBIALL_MASK >> + >> + /* Disable traps for BRBINJ instruction */ >> + orr x0, x0, #HFGITR_EL2_nBRBINJ_MASK >> + >> +.Lskip_brbe_insn_fgt_\@: >> +#endif /* CONFIG_ARM64_BRBE */ >> + msr_s SYS_HFGITR_EL2, x0 >> >> mrs x1, id_aa64pfr0_el1 // AMU traps UNDEF without AMU >> ubfx x1, x1, #ID_AA64PFR0_EL1_AMU_SHIFT, #4 >> @@ -228,6 +309,9 @@ >> __init_el2_nvhe_idregs >> __init_el2_cptr >> __init_el2_fgt >> +#ifdef CONFIG_ARM64_BRBE >> + __init_el2_brbe >> +#endif > > This largely looks fine, but I note that we haven't bothered with > ifdeffery for PMU and SPE, so I suspect it might be worth getting rid of > the ifdeffery for BRBE. Sure, will drop the #ifdef > > Mark.