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

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 1f59d8ba97765026cbea4775ed62e3d87e0b91ad..01ce61b283a324c5e00ed36ae085c89db731bdf7 100644 (file)
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -90,6 +90,7 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 /* RMP page size */
 #define RMP_PG_SIZE_4K                 0
 #define RMP_PG_SIZE_2M                 1
+#define RMP_TO_PG_LEVEL(level)         (((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
 
 #define RMPADJUST_VMSA_PAGE_BIT                BIT(16)
 
@@ -245,8 +246,10 @@ static inline u64 sev_get_status(void) { return 0; }
 
 #ifdef CONFIG_KVM_AMD_SEV
 bool snp_probe_rmptable_info(void);
+int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level);
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }
+static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return -ENODEV; }
 #endif
 
 #endif

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 575a9ff046cb06bc0df554e2ec27ef074e453056..7669b2ff0ec78601a79b2559d2024d9989261702 100644 (file)
--- 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);