RE: [PATCH v6 2/2] arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo

[Kamlakant Patel]

Hi Bhupesh,

> -----Original Message-----
> From: kexec <kexec-bounces@xxxxxxxxxxxxxxxxxxx> On Behalf Of Bhupesh
> Sharma
> Sent: Thursday, May 14, 2020 12:23 AM
> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; x86@xxxxxxxxxx
> Cc: Mark Rutland <mark.rutland@xxxxxxx>; Kazuhito Hagio <k-
> hagio@xxxxxxxxxxxxx>; Steve Capper <steve.capper@xxxxxxx>; Catalin
> Marinas <catalin.marinas@xxxxxxx>; bhsharma@xxxxxxxxxx; Ard Biesheuvel
> <ard.biesheuvel@xxxxxxxxxx>; kexec@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; James Morse <james.morse@xxxxxxx>; Dave
> Anderson <anderson@xxxxxxxxxx>; bhupesh.linux@xxxxxxxxx; Will Deacon
> <will@xxxxxxxxxx>
> Subject: [PATCH v6 2/2] arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo
> 
> 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 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
> 
> 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
> Tested-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> Signed-off-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
> ---
>  Documentation/admin-guide/kdump/vmcoreinfo.rst | 11 +++++++++++
>  arch/arm64/include/asm/pgtable-hwdef.h         |  1 +
>  arch/arm64/kernel/crash_core.c                 | 10 ++++++++++
>  3 files changed, 22 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst
> b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> index 2a632020f809..2baad0bfb09d 100644
> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> @@ -404,6 +404,17 @@ KERNELPACMASK
>  The mask to extract the Pointer Authentication Code from a kernel virtual
> address.
> 
> +TCR_EL1.T1SZ
> +------------
> +
> +Indicates the size offset of the memory region addressed by TTBR1_EL1.
> +The region size is 2^(64-T1SZ) bytes.
> +
> +TTBR1_EL1 is the table base address register specified by ARMv8-A
> +architecture which is used to lookup the page-tables for the Virtual
> +addresses in the higher VA range (refer to ARMv8 ARM document for more
> +details).
> +
>  arm
>  ===
> 
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h
> b/arch/arm64/include/asm/pgtable-hwdef.h
> index 6bf5e650da78..a1861af97ac9 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -216,6 +216,7 @@
>  #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 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());
I tested this patch on top of upstream kernel v5.7 and I am getting "crash: cannot determine VA_BITS_ACTUAL" error with crash tool.
I looked into crash-utility source and it is expecting tcr_el1_t1sz not TCR_EL1_T1SZ.
Could you please check.

Thanks,
Kamlakant Patel
>  	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
>  	vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n",
> 
> 	system_supports_address_auth() ?
> --
> 2.7.4
> 
> 
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