[PATCH v6 38/39] s390/kmsan: Implement the architecture-specific functions

[Ilya Leoshkevich <iii@linux.ibm.com>]

arch_kmsan_get_meta_or_null() finds the lowcore shadow by querying the
prefix and calling kmsan_get_metadata() again.

kmsan_virt_addr_valid() delegates to virt_addr_valid().

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/include/asm/kmsan.h | 59 +++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 arch/s390/include/asm/kmsan.h

diff --git a/arch/s390/include/asm/kmsan.h b/arch/s390/include/asm/kmsan.h
new file mode 100644
index 000000000000..27db65fbf3f6
--- /dev/null
+++ b/arch/s390/include/asm/kmsan.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_KMSAN_H
+#define _ASM_S390_KMSAN_H
+
+#include <asm/lowcore.h>
+#include <asm/page.h>
+#include <linux/kmsan.h>
+#include <linux/mmzone.h>
+#include <linux/stddef.h>
+
+#ifndef MODULE
+
+static inline bool is_lowcore_addr(void *addr)
+{
+	return addr >= (void *)&S390_lowcore &&
+	       addr < (void *)(&S390_lowcore + 1);
+}
+
+static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
+{
+	if (is_lowcore_addr(addr)) {
+		/*
+		 * Different lowcores accessed via S390_lowcore are described
+		 * by the same struct page. Resolve the prefix manually in
+		 * order to get a distinct struct page.
+		 */
+		addr += (void *)lowcore_ptr[raw_smp_processor_id()] -
+			(void *)&S390_lowcore;
+		if (KMSAN_WARN_ON(is_lowcore_addr(addr)))
+			return NULL;
+		return kmsan_get_metadata(addr, is_origin);
+	}
+	return NULL;
+}
+
+static inline bool kmsan_virt_addr_valid(void *addr)
+{
+	bool ret;
+
+	/*
+	 * pfn_valid() relies on RCU, and may call into the scheduler on exiting
+	 * the critical section. However, this would result in recursion with
+	 * KMSAN. Therefore, disable preemption here, and re-enable preemption
+	 * below while suppressing reschedules to avoid recursion.
+	 *
+	 * Note, this sacrifices occasionally breaking scheduling guarantees.
+	 * Although, a kernel compiled with KMSAN has already given up on any
+	 * performance guarantees due to being heavily instrumented.
+	 */
+	preempt_disable();
+	ret = virt_addr_valid(addr);
+	preempt_enable_no_resched();
+
+	return ret;
+}
+
+#endif /* !MODULE */
+
+#endif /* _ASM_S390_KMSAN_H */
-- 
2.45.1