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

[Bhupesh Sharma]

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