From 37fb60f8e3f011c25c120081a73886ad8dbc42fd Mon Sep 17 00:00:00 2001 From: James Hogan Date: Wed, 11 May 2016 13:50:50 +0100 Subject: [PATCH] MIPS: Add defs & probing of extended CP0_EBase The CP0_EBase register may optionally have a write gate (WG) bit to allow the upper bits to be written, i.e. bits 31:30 on MIPS32 since r3 (to allow for an exception base outside of KSeg0/KSeg1 when segmentation control is in use) and bits 63:30 on MIPS64 (which also implies the extension of CP0_EBase to 64 bits long). The presence of this feature will need to be known about for VZ support in order to correctly save and restore all the bits of the guest CP0_EBase register, so add CPU feature definition and probing for this feature. Probing the WG bit on MIPS64 can be a bit fiddly, since 64-bit COP0 register access instructions were UNDEFINED for 32-bit registers prior to MIPS r6, and it'd be nice to be able to probe without clobbering the existing state, so there are 3 potential paths: - If we do a 32-bit read of CP0_EBase and the WG bit is already set, the register must be 64-bit. - On MIPS r6 we can do a 64-bit read-modify-write to set CP0_EBase.WG, since the upper bits will read 0 and be ignored on write if the register is 32-bit. - On pre-r6 cores, we do a 32-bit read-modify-write of CP0_EBase. This avoids the potentially UNDEFINED behaviour, but will clobber the upper 32-bits of CP0_EBase if it isn't a simple sign extension (which also requires us to ensure BEV=1 or modifying the exception base would be UNDEFINED too). It is hopefully unlikely a bootloader would set up CP0_EBase to a 64-bit segment and leave WG=0. [ralf@linux-mips.org: Resolved merge conflict.] Signed-off-by: James Hogan Tested-by: Matt Redfearn Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/13223/ Signed-off-by: Ralf Baechle --- arch/mips/include/asm/cpu-features.h | 4 ++++ arch/mips/include/asm/cpu.h | 1 + arch/mips/include/asm/mipsregs.h | 3 +++ arch/mips/kernel/cpu-probe.c | 35 ++++++++++++++++++++++++++++ 4 files changed, 43 insertions(+) diff --git a/arch/mips/include/asm/cpu-features.h b/arch/mips/include/asm/cpu-features.h index bff73c52b273..676a37b9c37e 100644 --- a/arch/mips/include/asm/cpu-features.h +++ b/arch/mips/include/asm/cpu-features.h @@ -438,4 +438,8 @@ #define cpu_has_nan_2008 (cpu_data[0].options & MIPS_CPU_NAN_2008) #endif +#ifndef cpu_has_ebase_wg +# define cpu_has_ebase_wg (cpu_data[0].options & MIPS_CPU_EBASE_WG) +#endif + #endif /* __ASM_CPU_FEATURES_H */ diff --git a/arch/mips/include/asm/cpu.h b/arch/mips/include/asm/cpu.h index f6cecc52a8c6..3108d9b35bf1 100644 --- a/arch/mips/include/asm/cpu.h +++ b/arch/mips/include/asm/cpu.h @@ -404,6 +404,7 @@ enum cpu_type_enum { #define MIPS_CPU_VP MBIT_ULL(40) /* MIPSr6 Virtual Processors (multi-threading) */ #define MIPS_CPU_LDPTE MBIT_ULL(41) /* CPU has ldpte/lddir instructions */ #define MIPS_CPU_MVH MBIT_ULL(42) /* CPU supports MFHC0/MTHC0 */ +#define MIPS_CPU_EBASE_WG MBIT_ULL(43) /* CPU has EBase.WG */ /* * CPU ASE encodings diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h index 57d72f2bf745..4e8ad9d6038a 100644 --- a/arch/mips/include/asm/mipsregs.h +++ b/arch/mips/include/asm/mipsregs.h @@ -1458,6 +1458,9 @@ do { \ #define read_c0_ebase() __read_32bit_c0_register($15, 1) #define write_c0_ebase(val) __write_32bit_c0_register($15, 1, val) +#define read_c0_ebase_64() __read_64bit_c0_register($15, 1) +#define write_c0_ebase_64(val) __write_64bit_c0_register($15, 1, val) + #define read_c0_cdmmbase() __read_ulong_c0_register($15, 2) #define write_c0_cdmmbase(val) __write_ulong_c0_register($15, 2, val) diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c index 46a24729fbba..6a1a7da4b2d2 100644 --- a/arch/mips/kernel/cpu-probe.c +++ b/arch/mips/kernel/cpu-probe.c @@ -860,6 +860,41 @@ static void decode_configs(struct cpuinfo_mips *c) if (ok) ok = decode_config5(c); + /* Probe the EBase.WG bit */ + if (cpu_has_mips_r2_r6) { + u64 ebase; + unsigned int status; + + /* {read,write}_c0_ebase_64() may be UNDEFINED prior to r6 */ + ebase = cpu_has_mips64r6 ? read_c0_ebase_64() + : (s32)read_c0_ebase(); + if (ebase & MIPS_EBASE_WG) { + /* WG bit already set, we can avoid the clumsy probe */ + c->options |= MIPS_CPU_EBASE_WG; + } else { + /* Its UNDEFINED to change EBase while BEV=0 */ + status = read_c0_status(); + write_c0_status(status | ST0_BEV); + irq_enable_hazard(); + /* + * On pre-r6 cores, this may well clobber the upper bits + * of EBase. This is hard to avoid without potentially + * hitting UNDEFINED dm*c0 behaviour if EBase is 32-bit. + */ + if (cpu_has_mips64r6) + write_c0_ebase_64(ebase | MIPS_EBASE_WG); + else + write_c0_ebase(ebase | MIPS_EBASE_WG); + back_to_back_c0_hazard(); + /* Restore BEV */ + write_c0_status(status); + if (read_c0_ebase() & MIPS_EBASE_WG) { + c->options |= MIPS_CPU_EBASE_WG; + write_c0_ebase(ebase); + } + } + } + mips_probe_watch_registers(c); #ifndef CONFIG_MIPS_CPS -- 2.34.1