Allow user to pass desired page size via command line as either "arm64.pagesize=4k", "arm64.pagesize=16k", or "arm64.pagesize=64k". The specified value is stored in the SW_FEATURE register as an encoded page shift in a 4 bit field. We only allow setting the page size override if the requested size is supported by the HW and is within the compile-time [PAGE_SIZE_MIN, PAGE_SIZE_MAX] range. This second condition means that overrides get ignored when we have a compile-time page size (because PAGE_SIZE_MIN == PAGE_SIZE_MAX). Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> --- ***NOTE*** Any confused maintainers may want to read the cover note here for context: https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@xxxxxxx/ arch/arm64/include/asm/cpufeature.h | 11 ++++++++ arch/arm64/kernel/pi/idreg-override.c | 36 +++++++++++++++++++++++++++ 2 files changed, 47 insertions(+) diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 5584342672715..4edbb586810d7 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -18,6 +18,7 @@ #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR 0 #define ARM64_SW_FEATURE_OVERRIDE_HVHE 4 #define ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF 8 +#define ARM64_SW_FEATURE_OVERRIDE_PAGESHIFT 12 #ifndef __ASSEMBLY__ @@ -963,6 +964,16 @@ static inline bool arm64_test_sw_feature_override(int feat) &arm64_sw_feature_override); } +static inline int arm64_pageshift_cmdline(void) +{ + int val; + + val = arm64_apply_feature_override(0, + ARM64_SW_FEATURE_OVERRIDE_PAGESHIFT, + 4, &arm64_sw_feature_override); + return val ? val * 2 + 10 : 0; +} + static inline bool kaslr_disabled_cmdline(void) { return arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_NOKASLR); diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c index 29d4b6244a6f6..5a38bdb231bc8 100644 --- a/arch/arm64/kernel/pi/idreg-override.c +++ b/arch/arm64/kernel/pi/idreg-override.c @@ -183,6 +183,38 @@ static bool __init hvhe_filter(u64 val) ID_AA64MMFR1_EL1_VH_SHIFT)); } +static bool __init pageshift_filter(u64 val) +{ + u64 mmfr0 = read_sysreg_s(SYS_ID_AA64MMFR0_EL1); + u32 tgran64 = SYS_FIELD_GET(ID_AA64MMFR0_EL1, TGRAN64, mmfr0); + u32 tgran16 = SYS_FIELD_GET(ID_AA64MMFR0_EL1, TGRAN16, mmfr0); + u32 tgran4 = SYS_FIELD_GET(ID_AA64MMFR0_EL1, TGRAN4, mmfr0); + + /* pageshift is stored compressed in 4 bit field. */ + if (val) + val = val * 2 + 10; + + if (val < PAGE_SHIFT_MIN || val > PAGE_SHIFT_MAX) + return false; + + if (val == ARM64_PAGE_SHIFT_64K && + tgran64 >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN && + tgran64 <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX) + return true; + + if (val == ARM64_PAGE_SHIFT_16K && + tgran16 >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN && + tgran16 <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX) + return true; + + if (val == ARM64_PAGE_SHIFT_4K && + tgran4 >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN && + tgran4 <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX) + return true; + + return false; +} + static const struct ftr_set_desc sw_features __prel64_initconst = { .name = "arm64_sw", .override = &arm64_sw_feature_override, @@ -190,6 +222,7 @@ static const struct ftr_set_desc sw_features __prel64_initconst = { FIELD("nokaslr", ARM64_SW_FEATURE_OVERRIDE_NOKASLR, NULL), FIELD("hvhe", ARM64_SW_FEATURE_OVERRIDE_HVHE, hvhe_filter), FIELD("rodataoff", ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF, NULL), + FIELD("pageshift", ARM64_SW_FEATURE_OVERRIDE_PAGESHIFT, pageshift_filter), {} }, }; @@ -225,6 +258,9 @@ static const struct { { "rodata=off", "arm64_sw.rodataoff=1" }, { "arm64.nolva", "id_aa64mmfr2.varange=0" }, { "arm64.no32bit_el0", "id_aa64pfr0.el0=1" }, + { "arm64.pagesize=4k", "arm64_sw.pageshift=1" }, + { "arm64.pagesize=16k", "arm64_sw.pageshift=2" }, + { "arm64.pagesize=64k", "arm64_sw.pageshift=3" }, }; static int __init parse_hexdigit(const char *p, u64 *v) -- 2.43.0
