linux-kernel - [PATCH v2] riscv: Extend sv39 linear mapping max size to 128G

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Date: Sun, 30 Jun 2024 12:05:49 +0100
From: Stuart Menefy <stuart.menefy@...asip.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>,
	Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>
Cc: Stuart Menefy <stuart.menefy@...asip.com>,
	linux-doc@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] riscv: Extend sv39 linear mapping max size to 128G

This harmonizes all virtual addressing modes which can now all map
(PGDIR_SIZE * PTRS_PER_PGD) / 4 of physical memory.

The RISCV implementation of KASAN requires that the boundary between
shallow mappings are aligned on an 8G boundary. In this case we need
VMALLOC_START to be 8G aligned. So although we only need to move the
start of the linear mapping down by 4GiB to allow 128GiB to be mapped,
we actually move it down by 8GiB (creating a 4GiB hole between the
linear mapping and KASAN shadow space) to maintain the alignment
requirement.

Signed-off-by: Stuart Menefy <stuart.menefy@...asip.com>
---

Changes since V1:
This is a modified version of the patch posted by Alexandre Ghiti
<alexghiti@...osinc.com> [1]. That version moved the start of the
liner mapping by 4GiB, but was subsequently found to trigger a problem
in the KASAN code [2]. By moving the start address by 8GiB alignment
requiremenents are maintained.

[1] https://lore.kernel.org/linux-riscv/20240514133614.87813-1-alexghiti@rivosinc.com/
[2] https://lore.kernel.org/linux-riscv/4011b34a-1b86-42c7-aaf6-3bd297149f06@ghiti.fr/

---
 Documentation/arch/riscv/vm-layout.rst | 11 ++++++-----
 arch/riscv/include/asm/page.h          |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/Documentation/arch/riscv/vm-layout.rst b/Documentation/arch/riscv/vm-layout.rst
index e476b4386bd9..077b968dcc81 100644
--- a/Documentation/arch/riscv/vm-layout.rst
+++ b/Documentation/arch/riscv/vm-layout.rst
@@ -47,11 +47,12 @@ RISC-V Linux Kernel SV39
                                                               | Kernel-space virtual memory, shared between all processes:
   ____________________________________________________________|___________________________________________________________
                     |            |                  |         |
-   ffffffc6fea00000 | -228    GB | ffffffc6feffffff |    6 MB | fixmap
-   ffffffc6ff000000 | -228    GB | ffffffc6ffffffff |   16 MB | PCI io
-   ffffffc700000000 | -228    GB | ffffffc7ffffffff |    4 GB | vmemmap
-   ffffffc800000000 | -224    GB | ffffffd7ffffffff |   64 GB | vmalloc/ioremap space
-   ffffffd800000000 | -160    GB | fffffff6ffffffff |  124 GB | direct mapping of all physical memory
+   ffffffc4fea00000 | -236    GB | ffffffc4feffffff |    6 MB | fixmap
+   ffffffc4ff000000 | -236    GB | ffffffc4ffffffff |   16 MB | PCI io
+   ffffffc500000000 | -236    GB | ffffffc5ffffffff |    4 GB | vmemmap
+   ffffffc600000000 | -232    GB | ffffffd5ffffffff |   64 GB | vmalloc/ioremap space
+   ffffffd600000000 | -168    GB | fffffff5ffffffff |  128 GB | direct mapping of all physical memory
+                    |            |                  |         |
    fffffff700000000 |  -36    GB | fffffffeffffffff |   32 GB | kasan
   __________________|____________|__________________|_________|____________________________________________________________
                                                               |
diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
index 115ac98b8d72..81d47fbbd927 100644
--- a/arch/riscv/include/asm/page.h
+++ b/arch/riscv/include/asm/page.h
@@ -37,7 +37,7 @@
  * define the PAGE_OFFSET value for SV48 and SV39.
  */
 #define PAGE_OFFSET_L4		_AC(0xffffaf8000000000, UL)
-#define PAGE_OFFSET_L3		_AC(0xffffffd800000000, UL)
+#define PAGE_OFFSET_L3		_AC(0xffffffd600000000, UL)
 #else
 #define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
 #endif /* CONFIG_64BIT */
-- 
2.43.0