From: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
To: x86@kernel.org
Cc: Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ard Biesheuvel <ardb@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Kees Cook <kees@kernel.org>, Rong Xu <xur@google.com>,
linux-kernel@vger.kernel.org,
Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>,
Jared White <jaredwhite@microsoft.com>
Subject: [PATCH v3] x86/mm/64: free the gap between BSS_MAIN and BSS_DECRYPTED
Date: Fri, 10 Jul 2026 07:50:13 -0400 [thread overview]
Message-ID: <20260710115013.2833626-1-hamzamahfooz@linux.microsoft.com> (raw)
This region is unused after mark_rodata_ro() and takes up, up to 2 MiB
of memory. So, free it in mark_rodata_ro().
Co-developed-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
---
v3: guard __start_bss_decrypted{,_gap} with CONFIG_AMD_MEM_ENCRYPT.
---
arch/x86/include/asm/sections.h | 1 +
arch/x86/kernel/vmlinux.lds.S | 2 ++
arch/x86/mm/init_64.c | 8 ++++++++
3 files changed, 11 insertions(+)
diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 30e8ee7006f9..1d6589bc0f68 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -8,6 +8,7 @@
extern char __relocate_kernel_start[], __relocate_kernel_end[];
extern char __brk_base[], __brk_limit[];
extern char __end_rodata_aligned[];
+extern char __start_bss_decrypted_gap[];
#if defined(CONFIG_X86_64)
extern char __end_rodata_hpage_align[];
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 74e336d7f9dd..e9856d947370 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -88,6 +88,8 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
* decrypted to avoid exposing more than we wish.
*/
#define BSS_DECRYPTED \
+ . = ALIGN(PAGE_SIZE); \
+ __start_bss_decrypted_gap = .; \
. = ALIGN(PMD_SIZE); \
__start_bss_decrypted = .; \
__pi___start_bss_decrypted = .; \
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index d57f29ca23a5..c34973ac3656 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1409,6 +1409,10 @@ void mark_rodata_ro(void)
unsigned long end = (unsigned long)__end_rodata_hpage_align;
unsigned long text_end = PFN_ALIGN(_etext);
unsigned long rodata_end = PFN_ALIGN(__end_rodata);
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ unsigned long bss_decrypted_gap_start = PFN_ALIGN(__start_bss_decrypted_gap);
+ unsigned long bss_decrypted_gap_stop = PFN_ALIGN(__start_bss_decrypted);
+#endif
unsigned long all_end;
printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
@@ -1446,6 +1450,10 @@ void mark_rodata_ro(void)
(void *)text_end, (void *)rodata_start);
free_kernel_image_pages("unused kernel image (rodata/data gap)",
(void *)rodata_end, (void *)_sdata);
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ free_kernel_image_pages("unused kernel image (bss_decrypted gap)",
+ (void *)bss_decrypted_gap_start, (void *)bss_decrypted_gap_stop);
+#endif
}
/*
--
2.55.0
next reply other threads:[~2026-07-10 11:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-10 11:50 Hamza Mahfooz [this message]
2026-07-11 4:52 ` [PATCH v3] x86/mm/64: free the gap between BSS_MAIN and BSS_DECRYPTED Borislav Petkov
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