From: Patrick Bridges <bridges@apu.cs.unm.edu>
Date: Wed, 11 Aug 2010 22:44:19 +0000 (-0600)
Subject: Added robust physical alignment check
X-Git-Url: http://v3vee.org/palacios/gitweb/gitweb.cgi?a=commitdiff_plain;h=6b3606622300e3f0d45f7b8388e4c625a644aa4f;p=palacios.git

Added robust physical alignment check
---

diff --git a/palacios/src/palacios/mmu/vmm_shdw_pg_tlb_64.h b/palacios/src/palacios/mmu/vmm_shdw_pg_tlb_64.h
index aff8034..8b30540 100644
--- a/palacios/src/palacios/mmu/vmm_shdw_pg_tlb_64.h
+++ b/palacios/src/palacios/mmu/vmm_shdw_pg_tlb_64.h
@@ -271,6 +271,43 @@ static int handle_pdpe_shadow_pagefault_64(struct guest_info * info, addr_t faul
     return 0;
 }
 
+// For an address on a page of size page_size, compute the actual alignment
+// of the physical page it maps to
+int compute_physical_alignment(addr_t va, addr_t pa, uint32_t page_size)
+{
+    addr_t va_offset, pa_base;
+    switch (page_size) {
+	case PAGE_SIZE_1GB:
+	    va_offset = PAGE_OFFSET_1GB(va);
+	    break;
+	case PAGE_SIZE_4MB:
+	    va_offset = PAGE_OFFSET_4MB(va);
+	    break;
+	case PAGE_SIZE_2MB:
+	    va_offset = PAGE_OFFSET_2MB(va);
+	    break;
+	case PAGE_SIZE_4KB:
+	    return 1;
+	default:
+	    PrintError("Invalid page size in %s.\n", __FUNCTION__);
+	    return 0;
+    }
+ 
+    pa_base = pa - va_offset;
+
+    if (PAGE_OFFSET_1GB(pa_base) == 0) {
+	 return PAGE_SIZE_1GB;
+    } else if (PAGE_OFFSET_4MB(pa_base) == 0) {
+	 return PAGE_SIZE_4MB;
+    } else if (PAGE_OFFSET_2MB(pa_base) == 0) {
+	return PAGE_SIZE_2MB;
+    } else if (PAGE_OFFSET_4KB(pa_base) == 0) {
+	return PAGE_SIZE_4KB;
+    } else {
+        PrintError("Incorrection alignment setup or calculation in %s.\n", __FUNCTION__);
+	return 0;
+    }
+}
 
 static int handle_pde_shadow_pagefault_64(struct guest_info * info, addr_t fault_addr, pf_error_t error_code,
 					  pde64_t * shadow_pd, pde64_t * guest_pd) {
@@ -339,12 +376,12 @@ static int handle_pde_shadow_pagefault_64(struct guest_info * info, addr_t fault
     if (shadow_pde_access == PT_ACCESS_NOT_PRESENT) {
         // Check if  we can use large pages and the guest memory is properly aligned
         // to potentially use a large page
-        if (info->use_large_pages && guest_pde->large_page 
-	    && (info->vm_info->mem_align >= PAGE_SIZE_2MB)) {
+        if (info->use_large_pages && guest_pde->large_page) {
             // Check underlying physical memory map to see if a large page is viable
 	    addr_t guest_pa = BASE_TO_PAGE_ADDR_2MB(((pde64_2MB_t *)guest_pde)->page_base_addr);
-	    uint32_t max_size = v3_get_max_page_size(info, guest_pa, PAGE_SIZE_2MB);
-	    if (max_size >= PAGE_SIZE_2MB) {
+	    if ((compute_physical_alignment(fault_addr, guest_pa, PAGE_SIZE_2MB) >= PAGE_SIZE_2MB)
+	        && (v3_get_max_page_size(info, guest_pa, PAGE_SIZE_2MB) >= PAGE_SIZE_2MB)) {
+	    	// should be able to use a large page.
 	        if (handle_2MB_shadow_pagefault_pde_64(info, fault_addr, error_code, shadow_pde_access,
 		 	 		               (pde64_2MB_t *)shadow_pde, (pde64_2MB_t *)guest_pde) ==  0) {
 	    	    return 0;
@@ -353,7 +390,7 @@ static int handle_pde_shadow_pagefault_64(struct guest_info * info, addr_t fault
 	            return -1;
 		}
 	    } else {
-		PrintDebug("Underlying physical memory map doesn't allow use of a large page.\n");
+		PrintDebug("Alignment or underlying physical memory map doesn't allow use of a large page.\n");
 	    }
 	    // Fallthrough to handle the region with small pages
 	}