dm: allow High BIOS to be modifiable by the guest

In order to support OVMF NV storage writeback, the High BIOS region in
the guest will behave as RAM and can be modified by OVMF itself. Give
the guest write permission to this page.

Tracked-On: #3413
Signed-off-by: Peter Fang <peter.fang@intel.com>
Acked-by: Yin Fengwei <fengwei.yin@intel.com>

Author: peterfang

devicemodel/core/hugetlb.c

@@ -773,9 +773,14 @@ int hugetlb_setup_memory(struct vmctx *ctx)
 
 	/* map ept for biosmem */
 	if (ctx->biosmem > 0) {
+		/*
+		 * The High BIOS region can behave as RAM and be
+		 * modified by the boot firmware itself (e.g. OVMF
+		 * NV data storage region).
+		 */
 		if (vm_map_memseg_vma(ctx, ctx->biosmem, 4 * GB - ctx->biosmem,
 			(uint64_t)(ctx->baseaddr + 4 * GB - ctx->biosmem),
-			PROT_READ | PROT_EXEC) < 0)
+			PROT_ALL) < 0)
 		goto err;
 	}