linux-kernel - [RFC PATCH 5/8] arm64/Kconfig: Drop support for 47-bit virtual addressing

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Message-ID: <20241030101803.2037606-15-ardb+git@google.com>
Date: Wed, 30 Oct 2024 11:18:09 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Ryan Roberts <ryan.roberts@....com>, 
	Anshuman Khandual <anshuman.khandual@....com>, Kees Cook <keescook@...omium.org>
Subject: [RFC PATCH 5/8] arm64/Kconfig: Drop support for 47-bit virtual addressing

From: Ard Biesheuvel <ardb@...nel.org>

Drop the separate 47-bit virtual address space configuration, which is
identical in practice to 52-bit VA configuration on all 16k pages
capable hardware currently in the field. For future hardware that does
implement support for 52-bit virtual addressing, this mode can be chosen
at boot by passing 'arm64.nolva' on the kernel command line.

This reduces the number of configurations that need to be supported and
validated.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/Kconfig | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 099b1a825b9f..7df7d24c767d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -380,7 +380,6 @@ config PGTABLE_LEVELS
 	default 2 if ARM64_16K_PAGES && ARM64_VA_BITS_36
 	default 2 if ARM64_64K_PAGES && ARM64_VA_BITS_42
 	default 3 if ARM64_4K_PAGES && ARM64_VA_BITS_39
-	default 3 if ARM64_16K_PAGES && ARM64_VA_BITS_47
 	default 3 if ARM64_64K_PAGES
 	default 4 if ARM64_16K_PAGES
 	default 5 if ARM64_4K_PAGES
@@ -412,12 +411,12 @@ config KASAN_SHADOW_OFFSET
 	hex
 	depends on KASAN_GENERIC || KASAN_SW_TAGS
 	default 0xdfff800000000000 if (ARM64_VA_BITS_48 || (ARM64_VA_BITS_52 && !ARM64_16K_PAGES)) && !KASAN_SW_TAGS
-	default 0xdfffc00000000000 if (ARM64_VA_BITS_47 || ARM64_VA_BITS_52) && ARM64_16K_PAGES && !KASAN_SW_TAGS
+	default 0xdfffc00000000000 if ARM64_VA_BITS_52 && ARM64_16K_PAGES && !KASAN_SW_TAGS
 	default 0xdffffe0000000000 if ARM64_VA_BITS_42 && !KASAN_SW_TAGS
 	default 0xdfffffc000000000 if ARM64_VA_BITS_39 && !KASAN_SW_TAGS
 	default 0xdffffff800000000 if ARM64_VA_BITS_36 && !KASAN_SW_TAGS
 	default 0xefff800000000000 if (ARM64_VA_BITS_48 || (ARM64_VA_BITS_52 && !ARM64_16K_PAGES)) && KASAN_SW_TAGS
-	default 0xefffc00000000000 if (ARM64_VA_BITS_47 || ARM64_VA_BITS_52) && ARM64_16K_PAGES && KASAN_SW_TAGS
+	default 0xefffc00000000000 if ARM64_VA_BITS_52 && ARM64_16K_PAGES && KASAN_SW_TAGS
 	default 0xeffffe0000000000 if ARM64_VA_BITS_42 && KASAN_SW_TAGS
 	default 0xefffffc000000000 if ARM64_VA_BITS_39 && KASAN_SW_TAGS
 	default 0xeffffff800000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
@@ -1354,10 +1353,6 @@ config ARM64_VA_BITS_42
 	bool "42-bit"
 	depends on PAGE_SIZE_64KB
 
-config ARM64_VA_BITS_47
-	bool "47-bit"
-	depends on PAGE_SIZE_16KB
-
 config ARM64_VA_BITS_48
 	bool "48-bit"
 	depends on PAGE_SIZE_16KB
@@ -1397,7 +1392,6 @@ config ARM64_VA_BITS
 	default 36 if ARM64_VA_BITS_36
 	default 39 if ARM64_VA_BITS_39
 	default 42 if ARM64_VA_BITS_42
-	default 47 if ARM64_VA_BITS_47
 	default 48 if ARM64_VA_BITS_48
 	default 52 if ARM64_VA_BITS_52
 
-- 
2.47.0.163.g1226f6d8fa-goog