vabits_actual variable on arm64 indicates the actual VA space size, and allows a single binary to support both 48-bit and 52-bit VA spaces. If the ARMv8.2-LVA optional feature is present, and we are running with a 64KB page size; then it is possible to use 52-bits of address space for both userspace and kernel addresses. However, any kernel binary that supports 52-bit must also be able to fall back to 48-bit at early boot time if the hardware feature is not present. Since TCR_EL1.T1SZ indicates the size offset of the memory region addressed by TTBR1_EL1 (and hence can be used for determining the vabits_actual value) it makes more sense to export the same in vmcoreinfo rather than vabits_actual variable, as the name of the variable can change in future kernel versions, but the architectural constructs like TCR_EL1.T1SZ can be used better to indicate intended specific fields to user-space. User-space utilities like makedumpfile and crash-utility, need to read/write this value from/to vmcoreinfo for determining if a virtual address lies in the linear map range. The user-space computation for determining whether an address lies in the linear map range is the same as we have in kernel-space: #define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1))) I have sent out user-space patches for makedumpfile and crash-utility to add features for obtaining vabits_actual value from TCR_EL1.T1SZ (see [0] and [1]). Akashi reported that he was able to use this patchset and the user-space changes to get user-space working fine with the 52-bit kernel VA changes (see [2]). [0]. http://lists.infradead.org/pipermail/kexec/2019-November/023966.html [1]. http://lists.infradead.org/pipermail/kexec/2019-November/024006.html [2]. http://lists.infradead.org/pipermail/kexec/2019-November/023992.html Cc: James Morse <james.morse@xxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Steve Capper <steve.capper@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> Cc: Dave Anderson <anderson@xxxxxxxxxx> Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: kexec@xxxxxxxxxxxxxxxxxxx Signed-off-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx> --- arch/arm64/include/asm/pgtable-hwdef.h | 1 + arch/arm64/kernel/crash_core.c | 9 +++++++++ 2 files changed, 10 insertions(+) diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h index d9fbd433cc17..d2e7aff5821e 100644 --- a/arch/arm64/include/asm/pgtable-hwdef.h +++ b/arch/arm64/include/asm/pgtable-hwdef.h @@ -215,6 +215,7 @@ #define TCR_TxSZ(x) (TCR_T0SZ(x) | TCR_T1SZ(x)) #define TCR_TxSZ_WIDTH 6 #define TCR_T0SZ_MASK (((UL(1) << TCR_TxSZ_WIDTH) - 1) << TCR_T0SZ_OFFSET) +#define TCR_T1SZ_MASK (((UL(1) << TCR_TxSZ_WIDTH) - 1) << TCR_T1SZ_OFFSET) #define TCR_EPD0_SHIFT 7 #define TCR_EPD0_MASK (UL(1) << TCR_EPD0_SHIFT) diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c index ca4c3e12d8c5..f78310ba65ea 100644 --- a/arch/arm64/kernel/crash_core.c +++ b/arch/arm64/kernel/crash_core.c @@ -7,6 +7,13 @@ #include <linux/crash_core.h> #include <asm/memory.h> +static inline u64 get_tcr_el1_t1sz(void); + +static inline u64 get_tcr_el1_t1sz(void) +{ + return (read_sysreg(tcr_el1) & TCR_T1SZ_MASK) >> TCR_T1SZ_OFFSET; +} + void arch_crash_save_vmcoreinfo(void) { VMCOREINFO_NUMBER(VA_BITS); @@ -15,5 +22,7 @@ void arch_crash_save_vmcoreinfo(void) kimage_voffset); vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n", PHYS_OFFSET); + vmcoreinfo_append_str("NUMBER(tcr_el1_t1sz)=0x%llx\n", + get_tcr_el1_t1sz()); vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset()); } -- 2.7.4
