+int psmash(struct page *page)
+{
+       unsigned long spa = page_to_pfn(page) << PAGE_SHIFT;
+       int ret;
+
+       if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+               return -ENXIO;
+
+       /* Retry if another processor is modifying the RMP entry. */
+       do {
+               /* Binutils version 2.36 supports the PSMASH mnemonic. */
+               asm volatile(".byte 0xF3, 0x0F, 0x01, 0xFF"
+                             : "=a"(ret)
+                             : "a"(spa)
+                             : "memory", "cc");
+       } while (ret == FAIL_INUSE);

Should there be some retry limit here for safety? Or do we know that
we'll never be stuck in this loop? Ditto for the loop in rmpupdate.

+
+       return ret;
+}
+EXPORT_SYMBOL_GPL(psmash);