linux-kernel - [PATCH v5 02/12] arch: export set_direct_map_valid

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Message-ID: <20250828093902.2719-3-roypat@amazon.co.uk>
Date: Thu, 28 Aug 2025 09:39:17 +0000
From: "Roy, Patrick" <roypat@...zon.co.uk>
To: "david@...hat.com" <david@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "Roy, Patrick" <roypat@...zon.co.uk>, "tabba@...gle.com"
	<tabba@...gle.com>, "ackerleytng@...gle.com" <ackerleytng@...gle.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "kvmarm@...ts.linux.dev"
	<kvmarm@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"rppt@...nel.org" <rppt@...nel.org>, "will@...nel.org" <will@...nel.org>,
	"vbabka@...e.cz" <vbabka@...e.cz>, "Cali, Marco" <xmarcalx@...zon.co.uk>,
	"Kalyazin, Nikita" <kalyazin@...zon.co.uk>, "Thomson, Jack"
	<jackabt@...zon.co.uk>, "Manwaring, Derek" <derekmn@...zon.com>
Subject: [PATCH v5 02/12] arch: export set_direct_map_valid_noflush to KVM
 module

Use the new per-module export functionality to allow KVM (and only KVM)
access to set_direct_map_valid_noflush(). This allows guest_memfd to
remove its memory from the direct map, even if KVM is built as a module.

Direct map removal gives guest_memfd the same protection that
memfd_secret enjoys, such as hardening against Spectre-like attacks
through in-kernel gadgets.

Signed-off-by: Patrick Roy <roypat@...zon.co.uk>
---
 arch/arm64/mm/pageattr.c     | 1 +
 arch/loongarch/mm/pageattr.c | 1 +
 arch/riscv/mm/pageattr.c     | 1 +
 arch/s390/mm/pageattr.c      | 1 +
 arch/x86/mm/pat/set_memory.c | 1 +
 5 files changed, 5 insertions(+)

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 04d4a8f676db..4f3cddfab9b0 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -291,6 +291,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 
 	return set_memory_valid(addr, nr, valid);
 }
+EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
 /*
diff --git a/arch/loongarch/mm/pageattr.c b/arch/loongarch/mm/pageattr.c
index f5e910b68229..d076bfd3fcbf 100644
--- a/arch/loongarch/mm/pageattr.c
+++ b/arch/loongarch/mm/pageattr.c
@@ -217,6 +217,7 @@ int set_direct_map_invalid_noflush(struct page *page)
 
 	return __set_memory(addr, 1, __pgprot(0), __pgprot(_PAGE_PRESENT | _PAGE_VALID));
 }
+EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");
 
 int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 {
diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
index 3f76db3d2769..6db31040cd66 100644
--- a/arch/riscv/mm/pageattr.c
+++ b/arch/riscv/mm/pageattr.c
@@ -400,6 +400,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 
 	return __set_memory((unsigned long)page_address(page), nr, set, clear);
 }
+EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
 static int debug_pagealloc_set_page(pte_t *pte, unsigned long addr, void *data)
diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
index 348e759840e7..8ffd9ef09bc6 100644
--- a/arch/s390/mm/pageattr.c
+++ b/arch/s390/mm/pageattr.c
@@ -413,6 +413,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 
 	return __set_memory((unsigned long)page_to_virt(page), nr, flags);
 }
+EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");
 
 bool kernel_page_present(struct page *page)
 {
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 8834c76f91c9..87e9c7d2dcdc 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2661,6 +2661,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 
 	return __set_pages_np(page, nr);
 }
+EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
 void __kernel_map_pages(struct page *page, int numpages, int enable)
-- 
2.50.1