efi: use directmap to access runtime services table

Do not require switching page tables to access (static) information in
the runtime services table itself, use directmap for this. This allows
exiting early from XEN_EFI_query_capsule_capabilities,
XEN_EFI_update_capsule and XEN_EFI_query_variable_info (in case of not
supported call) without all the impact of page table switch.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>

xen/common/efi/boot.c

@@ -1126,6 +1126,7 @@ static void __init efi_exit_boot(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *Syste
 
     /* Adjust pointers into EFI. */
     efi_ct = (void *)efi_ct + DIRECTMAP_VIRT_START;
+    efi_rs = (void *)efi_rs + DIRECTMAP_VIRT_START;
     efi_memmap = (void *)efi_memmap + DIRECTMAP_VIRT_START;
     efi_fw_vendor = (void *)efi_fw_vendor + DIRECTMAP_VIRT_START;
 }

xen/common/efi/runtime.c

@@ -211,12 +211,7 @@ int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
         break;
     case XEN_FW_EFI_RT_VERSION:
     {
-        struct efi_rs_state state = efi_rs_enter();
-
-        if ( !state.cr3 )
-            return -EOPNOTSUPP;
         info->version = efi_rs->Hdr.Revision;
-        efi_rs_leave(&state);
         break;
     }
     case XEN_FW_EFI_CONFIG_TABLE:
@@ -618,12 +613,11 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
             break;
         }
 
-        state = efi_rs_enter();
-        if ( !state.cr3 || (efi_rs->Hdr.Revision >> 16) < 2 )
-        {
-            efi_rs_leave(&state);
+        if ( (efi_rs->Hdr.Revision >> 16) < 2 )
+            return -EOPNOTSUPP;
+        state = efi_rs_enter();
+        if ( !state.cr3 )
             return -EOPNOTSUPP;
-        }
         status = efi_rs->QueryVariableInfo(
             op->u.query_variable_info.attr,
             &op->u.query_variable_info.max_store_size,
@@ -637,13 +631,8 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        state = efi_rs_enter();
-        if ( !state.cr3 || (efi_rs->Hdr.Revision >> 16) < 2 )
-        {
-            efi_rs_leave(&state);
+        if ( (efi_rs->Hdr.Revision >> 16) < 2 )
             return -EOPNOTSUPP;
-        }
-        efi_rs_leave(&state);
         /* XXX fall through for now */
     default:
         return -ENOSYS;