Re: [PATCH v6 2/2] arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo
From: James Morse <james.morse@arm.com>
Date: 2020-07-01 12:00:20
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Hi Bhupesh, On 13/05/2020 19:52, Bhupesh Sharma wrote:
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.
I'd prefer the commit message not to refer to this 'vabits_actual' thing at all. By the time a git-archaeologist comes to read this, it may be long gone. Ideally this would refer to: TCR_EL1.TxSZ, which controls the VA space size, and can be configured by a single kernel image to support either 48-bit or 52-bit VA space.
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 this value from vmcoreinfo for determining if a virtual address lies in the linear map range. While at it also add documentation for TCR_EL1.T1SZ variable being added to vmcoreinfo. It indicates the size offset of the memory region addressed by TTBR1_EL1
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c index 1f646b07e3e9..314391a156ee 100644 --- a/arch/arm64/kernel/crash_core.c +++ b/arch/arm64/kernel/crash_core.c@@ -7,6 +7,14 @@ #include <linux/crash_core.h> #include <asm/cpufeature.h> #include <asm/memory.h> +#include <asm/pgtable-hwdef.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) {@@ -16,6 +24,8 @@ 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()); vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n", system_supports_address_auth() ?
(I think second guessing the kernel memory map is a sisyphean effort), but this register isn't going to disappear, or change its meaning!: Reviewed-by: James Morse <james.morse@arm.com> You may need to re-post this to get the maintainer's attention as its normally safe to assume patches posted before rc1 no longer apply. (in this case, this one does) Thanks, James _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel