linux-kernel - [PATCH v2 2/2] mm/memory_hotplug: Add support to unaccept memory after hot-remove

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Message-ID: <20260112202300.43546-3-prsampat@amd.com>
Date: Mon, 12 Jan 2026 14:23:00 -0600
From: "Pratik R. Sampat" <prsampat@....com>
To: <linux-mm@...ck.org>, <linux-coco@...ts.linux.dev>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <kas@...nel.org>, <ardb@...nel.org>,
	<akpm@...ux-foundation.org>, <david@...nel.org>, <osalvador@...e.de>,
	<thomas.lendacky@....com>, <michael.roth@....com>, <prsampat@....com>
Subject: [PATCH v2 2/2] mm/memory_hotplug: Add support to unaccept memory after hot-remove

Transition memory to the shared state during a hot-remove operation so
that it can be re-used by the hypervisor. This also applies when memory
is intended to be hotplugged back in later, as those pages will need to
be re-accepted after crossing the trust boundary.

Signed-off-by: Pratik R. Sampat <prsampat@....com>
---
 arch/x86/coco/sev/core.c                 | 13 +++++++++++++
 arch/x86/include/asm/sev.h               |  2 ++
 arch/x86/include/asm/unaccepted_memory.h |  9 +++++++++
 mm/memory_hotplug.c                      |  3 +++
 4 files changed, 27 insertions(+)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 9ae3b11754e6..63d8f44b76eb 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -703,6 +703,19 @@ void snp_accept_memory(phys_addr_t start, phys_addr_t end)
 	set_pages_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE);
 }
 
+void snp_unaccept_memory(phys_addr_t start, phys_addr_t end)
+{
+	unsigned long vaddr, npages;
+
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return;
+
+	vaddr = (unsigned long)__va(start);
+	npages = (end - start) >> PAGE_SHIFT;
+
+	set_pages_state(vaddr, npages, SNP_PAGE_STATE_SHARED);
+}
+
 static int vmgexit_ap_control(u64 event, struct sev_es_save_area *vmsa, u32 apic_id)
 {
 	bool create = event != SVM_VMGEXIT_AP_DESTROY;
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 0e6c0940100f..3327de663793 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -514,6 +514,7 @@ bool snp_init(struct boot_params *bp);
 void snp_dmi_setup(void);
 int snp_issue_svsm_attest_req(u64 call_id, struct svsm_call *call, struct svsm_attest_call *input);
 void snp_accept_memory(phys_addr_t start, phys_addr_t end);
+void snp_unaccept_memory(phys_addr_t start, phys_addr_t end);
 u64 snp_get_unsupported_features(u64 status);
 u64 sev_get_status(void);
 void sev_show_status(void);
@@ -623,6 +624,7 @@ static inline int snp_issue_svsm_attest_req(u64 call_id, struct svsm_call *call,
 	return -ENOTTY;
 }
 static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
+static inline void snp_unaccept_memory(phys_addr_t start, phys_addr_t end) { }
 static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
 static inline u64 sev_get_status(void) { return 0; }
 static inline void sev_show_status(void) { }
diff --git a/arch/x86/include/asm/unaccepted_memory.h b/arch/x86/include/asm/unaccepted_memory.h
index f5937e9866ac..8715be843e65 100644
--- a/arch/x86/include/asm/unaccepted_memory.h
+++ b/arch/x86/include/asm/unaccepted_memory.h
@@ -18,6 +18,15 @@ static inline void arch_accept_memory(phys_addr_t start, phys_addr_t end)
 	}
 }
 
+static inline void arch_unaccept_memory(phys_addr_t start, phys_addr_t end)
+{
+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {
+		snp_unaccept_memory(start, end);
+	} else {
+		panic("Cannot unaccept memory: unknown platform\n");
+	}
+}
+
 static inline struct efi_unaccepted_memory *efi_get_unaccepted_table(void)
 {
 	if (efi.unaccepted == EFI_INVALID_TABLE_ADDR)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8cfbf0541430..718f729cf687 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -2242,6 +2242,9 @@ static int try_remove_memory(u64 start, u64 size)
 
 	mem_hotplug_begin();
 
+	if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY))
+		arch_unaccept_memory(start, start + size);
+
 	rc = memory_blocks_have_altmaps(start, size);
 	if (rc < 0) {
 		mem_hotplug_done();
-- 
2.52.0