From: Ashish Kalra <ashish.kalra@amd.com>

Pages are unsafe to be released back to the page-allocator, if they
have been transitioned to firmware/guest state and can't be reclaimed
or transitioned back to hypervisor/shared state. In this case add
them to an internal leaked pages list to ensure that they are not freed
or touched/accessed to cause fatal page faults.

Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
[mdr: relocate to arch/x86/coco/sev/host.c]
Signed-off-by: Michael Roth <redacted>
---
 arch/x86/coco/sev/host.c        | 28 ++++++++++++++++++++++++++++
 arch/x86/include/asm/sev-host.h |  3 +++
 2 files changed, 31 insertions(+)

diff --git a/arch/x86/coco/sev/host.c b/arch/x86/coco/sev/host.c
index cd3b4c6a25bc..373e91f5a337 100644
--- a/arch/x86/coco/sev/host.c
+++ b/arch/x86/coco/sev/host.c

@@ -64,6 +64,12 @@ struct rmpentry {
 static unsigned long rmptable_start __ro_after_init;
 static unsigned long rmptable_end __ro_after_init;
 
+/* list of pages which are leaked and cannot be reclaimed */
+static LIST_HEAD(snp_leaked_pages_list);
+static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);
+
+static atomic_long_t snp_nr_leaked_pages = ATOMIC_LONG_INIT(0);
+
 #undef pr_fmt
 #define pr_fmt(fmt)	"SEV-SNP: " fmt
 

@@ -494,3 +500,25 @@ int rmp_make_shared(u64 pfn, enum pg_level level)
 	return rmpupdate(pfn, &val);
 }
 EXPORT_SYMBOL_GPL(rmp_make_shared);
+
+void snp_leak_pages(unsigned long pfn, unsigned int npages)
+{
+	struct page *page = pfn_to_page(pfn);
+
+	WARN(1, "psc failed, pfn 0x%lx pages %d (marked offline)\n", pfn, npages);
+
+	spin_lock(&snp_leaked_pages_list_lock);
+	while (npages--) {
+		/*
+		 * Reuse the page's buddy list for chaining into the leaked
+		 * pages list. This page should not be on a free list currently
+		 * and is also unsafe to be added to a free list.
+		 */
+		list_add_tail(&page->buddy_list, &snp_leaked_pages_list);
+		sev_dump_rmpentry(pfn);
+		pfn++;
+	}
+	spin_unlock(&snp_leaked_pages_list_lock);
+	atomic_long_inc(&snp_nr_leaked_pages);
+}
+EXPORT_SYMBOL_GPL(snp_leak_pages);

diff --git a/arch/x86/include/asm/sev-host.h b/arch/x86/include/asm/sev-host.h
index 753e80d16433..bab3b226777a 100644
--- a/arch/x86/include/asm/sev-host.h
+++ b/arch/x86/include/asm/sev-host.h

@@ -19,6 +19,8 @@ void sev_dump_rmpentry(u64 pfn);
 int psmash(u64 pfn);
 int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid, bool immutable);
 int rmp_make_shared(u64 pfn, enum pg_level level);
+void snp_leak_pages(unsigned long pfn, unsigned int npages);
+
 #else
 static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return 0; }
 static inline void sev_dump_rmpentry(u64 pfn) {}

@@ -29,6 +31,7 @@ static inline int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int as
 	return -ENODEV;
 }
 static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV; }
+void snp_leak_pages(unsigned long pfn, unsigned int npages) {}