[RFC PATCH 4/4] mm: Add support for unaccepted memory hot-remove

["Pratik R. Sampat" <prsampat@amd.com>]

Transition memory to shared during a hot-remove operation so that it can
be re-used by the hypervisor. During lazy acceptance, only memory that
was used has been accepted, therefore during hot-remove only mark pages
as shared that were previously accepted / made private.

Signed-off-by: Pratik R. Sampat <prsampat@amd.com>
---
 arch/x86/coco/sev/core.c                 | 23 +++++++++++++++
 arch/x86/include/asm/sev.h               |  2 ++
 arch/x86/include/asm/unaccepted_memory.h |  9 ++++++
 drivers/firmware/efi/unaccepted_memory.c | 37 ++++++++++++++++++++++++
 include/linux/mm.h                       |  7 +++++
 mm/memory_hotplug.c                      |  2 ++
 6 files changed, 80 insertions(+)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index a5c9615a6e0c..c05fc91d10a1 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -621,6 +621,29 @@ void snp_accept_memory(phys_addr_t start, phys_addr_t end)
 	set_pages_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE, 0);
 }
 
+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;
+
+	/*
+	 * Hotplugged memory can be set to shared externally. Attempting to
+	 * re-share the memory (during hot-remove) will cause the pvalidate
+	 * operation to not make any changes to the RMP table triggering the
+	 * PVALIDATE_FAIL_NOUPDATE condition
+	 *
+	 * Since the memory hotplug case is unique, specify this intent so that
+	 * if the page is part of hotplugged memory a pvalidate rescind
+	 * operation is not performed
+	 */
+	set_pages_state(vaddr, npages, SNP_PAGE_STATE_SHARED, SNP_PSC_SHARED_TO_SHARED);
+}
+
 int snp_extend_hotplug_memory_state_bitmap(phys_addr_t start,
 					   unsigned long size,
 					   uint64_t unit_size)
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index eb605892645c..8f3c5b878fd7 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -547,6 +547,7 @@ void __noreturn snp_abort(void);
 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);
@@ -639,6 +640,7 @@ 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 abdf5472de9e..ad392294b71b 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 accept 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/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
index 6796042a64aa..662cf0d6715f 100644
--- a/drivers/firmware/efi/unaccepted_memory.c
+++ b/drivers/firmware/efi/unaccepted_memory.c
@@ -301,6 +301,43 @@ int accept_hotplug_memory(phys_addr_t mem_range_start, unsigned long mem_range_s
 	return 0;
 }
 
+void unaccept_hotplug_memory(phys_addr_t mem_range_start, unsigned long mem_range_size)
+{
+	u64 unit_size, phys_base, bit_start, bit_end, addr;
+	struct efi_unaccepted_memory *unacc_tbl;
+	unsigned long flags, *bitmap;
+	phys_addr_t start, end;
+	int i;
+
+	unacc_tbl = efi_get_unaccepted_table();
+	if (!unacc_tbl)
+		return;
+
+	phys_base = unacc_tbl->phys_base;
+	unit_size = unacc_tbl->unit_size;
+
+	start = mem_range_start - phys_base;
+	end = (mem_range_start + mem_range_size) - phys_base;
+
+	bit_start = start / unit_size;
+	bit_end = end / unit_size;
+
+	/* Only unaccept memory that was previously accepted in the range */
+	for (i = bit_start; i < bit_end; i++) {
+		spin_lock_irqsave(&unaccepted_memory_lock, flags);
+		bitmap = efi_get_unaccepted_bitmap();
+		if (!bitmap || test_bit(i, bitmap)) {
+			spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
+			continue;
+		}
+
+		addr = phys_base + i * unit_size;
+
+		arch_unaccept_memory(addr, addr + unit_size);
+		spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
+	}
+}
+
 #ifdef CONFIG_PROC_VMCORE
 static bool unaccepted_memory_vmcore_pfn_is_ram(struct vmcore_cb *cb,
 						unsigned long pfn)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bb43876e6c47..34d48693dc86 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4079,6 +4079,8 @@ bool range_contains_unaccepted_memory(phys_addr_t start, unsigned long size);
 void accept_memory(phys_addr_t start, unsigned long size);
 int accept_hotplug_memory(phys_addr_t mem_range_start,
 			  unsigned long mem_range_size);
+void unaccept_hotplug_memory(phys_addr_t mem_range_start,
+			     unsigned long mem_range_size);
 bool mm_lazy_accept_enabled(void);
 
 #else
@@ -4099,6 +4101,11 @@ static inline int accept_hotplug_memory(phys_addr_t mem_range_start,
 	return 0;
 }
 
+static inline void unaccept_hotplug_memory(phys_addr_t mem_range_start,
+					   unsigned long mem_range_size)
+{
+}
+
 static inline bool mm_lazy_accept_enabled(void) { return false; }
 
 #endif
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index bf8086682b66..0b14b14e53fe 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -2254,6 +2254,8 @@ static int try_remove_memory(u64 start, u64 size)
 
 	mem_hotplug_begin();
 
+	unaccept_hotplug_memory(start, size);
+
 	rc = memory_blocks_have_altmaps(start, size);
 	if (rc < 0) {
 		mem_hotplug_done();
-- 
2.51.1