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
> 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@xxxxxxx>
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
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