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

[Amit Kachhap]

Hi Bhupesh,

On 5/14/20 12:22 AM, 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.
>
> 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>

I tested this for both 48 and 52 VA. The dump log looks fine with the 
crash tool link provided by you so,

Tested-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>

Also the code changes/documentation looks fine to me with a minor 
comments below,

Reviewed-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>

> ---
>   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>

Nit: May be you forgot to include <asm/sysreg.h> here as suggested by 
James in v5.

Cheers,
Amit

> +
> +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() ?