On 16/07/2021 08:06, Anshuman Khandual wrote:

On 7/14/21 1:51 PM, Suzuki K Poulose wrote:

quoted

On 14/07/2021 03:21, Anshuman Khandual wrote:

quoted

Detect FEAT_LPA2 implementation early enough during boot when requested via
CONFIG_ARM64_PA_BITS_52_LPA2 and remember in a variable arm64_lpa2_enabled.
This variable could then be used to turn on TCR_EL1.TCR_DS effecting the 52
bits PA range or fall back to default 48 bits PA range if FEAT_LPA2 feature
was requested but found not to be implemented.

Signed-off-by: Anshuman Khandual <redacted>
---
   arch/arm64/include/asm/memory.h |  1 +
   arch/arm64/kernel/head.S        | 15 +++++++++++++++
   arch/arm64/mm/mmu.c             |  3 +++
   arch/arm64/mm/proc.S            |  9 +++++++++
   4 files changed, 28 insertions(+)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 824a365..d0ca002 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h

@@ -178,6 +178,7 @@
   #include <asm/bug.h>
     extern u64            vabits_actual;
+extern u64            arm64_lpa2_enabled;
     extern s64            memstart_addr;
   /* PHYS_OFFSET - the physical address of the start of memory. */

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 6444147..9cf79ea 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S

@@ -94,6 +94,21 @@ SYM_CODE_START(primary_entry)
       adrp    x23, __PHYS_OFFSET
       and    x23, x23, MIN_KIMG_ALIGN - 1    // KASLR offset, defaults to 0
       bl    set_cpu_boot_mode_flag
+
+#ifdef CONFIG_ARM64_PA_BITS_52_LPA2
+    mrs     x10, ID_AA64MMFR0_EL1
+    ubfx    x10, x10, #ID_AA64MMFR0_TGRAN_SHIFT, 4
+    cmp     x10, #ID_AA64MMFR0_TGRAN_LPA2
+    b.ne    1f

For the sake of forward compatibility, this should be "b.lt"

Right, I guess we could assume that the feature will be present from the
current ID_AA64MMFR0_TGRAN_LPA2 values onward in the future. But should
not this also be capped at ID_AA64MMFR0_TGRAN_SUPPORTED_MAX as the upper
limit is different for 4K and 16K page sizes.

Absolutely.

Cheers
Suzuki