x86/sev: Add RMP entry lookup helpers

Add a helper that can be used to access information contained in the RMP
entry corresponding to a particular PFN. This will be needed to make
decisions on how to handle setting up mappings in the NPT in response to
guest page-faults and handling things like cleaning up pages and setting
them back to the default hypervisor-owned state when they are no longer
being used for private data.

  [ mdr: separate 'assigned' indicator from return code, and simplify
    function signatures for various helpers. ]

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240126041126.1927228-7-michael.roth@amd.com

1 files changed, 49 insertions, 0 deletions

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 575a9ff046cb..7669b2ff0ec7 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -53,6 +53,9 @@ struct rmpentry {
  */
 #define RMPTABLE_CPU_BOOKKEEPING_SZ	0x4000
 
+/* Mask to apply to a PFN to get the first PFN of a 2MB page */
+#define PFN_PMD_MASK	GENMASK_ULL(63, PMD_SHIFT - PAGE_SHIFT)
+
 static u64 probed_rmp_base, probed_rmp_size;
 static struct rmpentry *rmptable __ro_after_init;
 static u64 rmptable_max_pfn __ro_after_init;
@@ -214,3 +217,49 @@ nosnp:
  * This must be called after the IOMMU has been initialized.
  */
 device_initcall(snp_rmptable_init);
+
+static struct rmpentry *get_rmpentry(u64 pfn)
+{
+	if (WARN_ON_ONCE(pfn > rmptable_max_pfn))
+		return ERR_PTR(-EFAULT);
+
+	return &rmptable[pfn];
+}
+
+static struct rmpentry *__snp_lookup_rmpentry(u64 pfn, int *level)
+{
+	struct rmpentry *large_entry, *entry;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		return ERR_PTR(-ENODEV);
+
+	entry = get_rmpentry(pfn);
+	if (IS_ERR(entry))
+		return entry;
+
+	/*
+	 * Find the authoritative RMP entry for a PFN. This can be either a 4K
+	 * RMP entry or a special large RMP entry that is authoritative for a
+	 * whole 2M area.
+	 */
+	large_entry = get_rmpentry(pfn & PFN_PMD_MASK);
+	if (IS_ERR(large_entry))
+		return large_entry;
+
+	*level = RMP_TO_PG_LEVEL(large_entry->pagesize);
+
+	return entry;
+}
+
+int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level)
+{
+	struct rmpentry *e;
+
+	e = __snp_lookup_rmpentry(pfn, level);
+	if (IS_ERR(e))
+		return PTR_ERR(e);
+
+	*assigned = !!e->assigned;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);