Re: [PATCH] support 1gb pages in guest page table walker

[Christoph Egger <Christoph.Egger@amd.com>]

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On 07/25/11 12:30, Tim Deegan wrote:
> At 11:25 +0100 on 25 Jul (1311593146), Tim Deegan wrote:
>> Also this function should be called from the CPUID trap handler to make
>> sure we never advertise PSE1GB when we're not going to support it.
>
> Er, not this function exactly, since CPUID should report the feature
> even when the guest's not in long_mode.  I think it needs a
> hvm_pse1G_supported that can be called from CPUID, and then
> guest_supports_1G_superpages() boils down to
> "(GUEST_PAGING_LEVEL>= 4)&&  hvm_pse1G_supported(v)"

New version attached. I removed the fake l1e calculation.
Something is still wrong: The l2 guest kernel crashes with
an unexpected null pointer derefencing but it boots w/o
this patch.

Is it a problem when l1 guest uses 1gb pages where the host
uses 4k or 2m pages?

Christoph


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# HG changeset patch
# User cegger
# Date 1311681725 -7200
support 1gb pages for guests

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>

diff -r 4f2c59fb28e6 -r 6d15152fb59a xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2389,6 +2389,7 @@ void hvm_cpuid(unsigned int input, unsig
                                    unsigned int *ecx, unsigned int *edx)
 {
     struct vcpu *v = current;
+    struct domain *d = v->domain;
     unsigned int count = *ecx;
 
     if ( cpuid_viridian_leaves(input, eax, ebx, ecx, edx) )
@@ -2397,7 +2398,7 @@ void hvm_cpuid(unsigned int input, unsig
     if ( cpuid_hypervisor_leaves(input, count, eax, ebx, ecx, edx) )
         return;
 
-    domain_cpuid(v->domain, input, *ecx, eax, ebx, ecx, edx);
+    domain_cpuid(d, input, *ecx, eax, ebx, ecx, edx);
 
     switch ( input )
     {
@@ -2433,7 +2434,7 @@ void hvm_cpuid(unsigned int input, unsig
             {
                 if ( !(v->arch.xcr0 & (1ULL << sub_leaf)) )
                     continue;
-                domain_cpuid(v->domain, input, sub_leaf, &_eax, &_ebx, &_ecx, 
+                domain_cpuid(d, input, sub_leaf, &_eax, &_ebx, &_ecx, 
                              &_edx);
                 if ( (_eax + _ebx) > *ebx )
                     *ebx = _eax + _ebx;
@@ -2444,9 +2445,13 @@ void hvm_cpuid(unsigned int input, unsig
     case 0x80000001:
         /* We expose RDTSCP feature to guest only when
            tsc_mode == TSC_MODE_DEFAULT and host_tsc_is_safe() returns 1 */
-        if ( v->domain->arch.tsc_mode != TSC_MODE_DEFAULT ||
+        if ( d->arch.tsc_mode != TSC_MODE_DEFAULT ||
              !host_tsc_is_safe() )
             *edx &= ~cpufeat_mask(X86_FEATURE_RDTSCP);
+        /* Expose 1gb page feature for HVM HAP guests and hw support is
+         * available. */
+        if (hvm_pse1gb_supported(d))
+            *edx |= cpufeat_mask(X86_FEATURE_PAGE1GB);
         break;
     }
 }
diff -r 4f2c59fb28e6 -r 6d15152fb59a xen/arch/x86/mm/guest_walk.c
--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -134,7 +134,8 @@ guest_walk_tables(struct vcpu *v, struct
     guest_l4e_t *l4p;
 #endif
     uint32_t gflags, mflags, iflags, rc = 0;
-    int pse, smep;
+    int smep;
+    bool_t pse1G = 0, pse2M = 0;
 
     perfc_incr(guest_walk);
     memset(gw, 0, sizeof(*gw));
@@ -182,6 +183,27 @@ guest_walk_tables(struct vcpu *v, struct
     if ( rc & _PAGE_PRESENT )
         goto out;
 
+    pse1G = (guest_supports_1G_superpages(v) && 
+           (guest_l3e_get_flags(gw->l3e) & _PAGE_PSE)); 
+
+    if ( pse1G )
+    {
+        /* Shadow paging doesn't support 1gb pages so a fake
+         * shadow l1 table entry is not needed. */
+        gfn_t start = guest_l3e_get_gfn(gw->l3e);
+
+#define GUEST_L3_GFN_ALIGN (1 << (GUEST_L3_PAGETABLE_SHIFT - \
+                                  GUEST_L2_PAGETABLE_SHIFT))
+        if ( gfn_x(start) & (GUEST_L3_GFN_ALIGN - 1) & ~0x1 )
+        {
+            rc |= _PAGE_INVALID_BITS;
+        }
+#undef GUEST_L3_GFN_ALIGN
+
+        gw->l2mfn = gw->l1mfn = _mfn(INVALID_MFN);
+        goto set_ad;
+    }
+
 #else /* PAE only... */
 
     /* Get the l3e and check its flag */
@@ -219,10 +241,10 @@ guest_walk_tables(struct vcpu *v, struct
     if ( rc & _PAGE_PRESENT )
         goto out;
 
-    pse = (guest_supports_superpages(v) && 
+    pse2M = (guest_supports_superpages(v) && 
            (guest_l2e_get_flags(gw->l2e) & _PAGE_PSE)); 
 
-    if ( pse )
+    if ( pse2M )
     {
         /* Special case: this guest VA is in a PSE superpage, so there's
          * no guest l1e.  We make one up so that the propagation code
@@ -282,6 +304,9 @@ guest_walk_tables(struct vcpu *v, struct
         rc |= ((gflags & mflags) ^ mflags);
     }
 
+#if GUEST_PAGING_LEVELS >= 4 /* 64-bit only... */
+set_ad:
+#endif
     /* Now re-invert the user-mode requirement for SMEP. */
     if ( smep ) 
         rc ^= _PAGE_USER;
@@ -295,17 +320,21 @@ guest_walk_tables(struct vcpu *v, struct
 #if GUEST_PAGING_LEVELS == 4 /* 64-bit only... */
         if ( set_ad_bits(l4p + guest_l4_table_offset(va), &gw->l4e, 0) )
             paging_mark_dirty(d, mfn_x(gw->l4mfn));
-        if ( set_ad_bits(l3p + guest_l3_table_offset(va), &gw->l3e, 0) )
+        if ( set_ad_bits(l3p + guest_l3_table_offset(va), &gw->l3e,
+                         (pse1G && (pfec & PFEC_write_access))) )
             paging_mark_dirty(d, mfn_x(gw->l3mfn));
 #endif
-        if ( set_ad_bits(l2p + guest_l2_table_offset(va), &gw->l2e,
-                         (pse && (pfec & PFEC_write_access))) )
-            paging_mark_dirty(d, mfn_x(gw->l2mfn));            
-        if ( !pse ) 
+        if ( !pse1G ) 
         {
-            if ( set_ad_bits(l1p + guest_l1_table_offset(va), &gw->l1e, 
-                             (pfec & PFEC_write_access)) )
-                paging_mark_dirty(d, mfn_x(gw->l1mfn));
+            if ( set_ad_bits(l2p + guest_l2_table_offset(va), &gw->l2e,
+                             (pse2M && (pfec & PFEC_write_access))) )
+                paging_mark_dirty(d, mfn_x(gw->l2mfn));            
+            if ( !pse2M ) 
+            {
+                if ( set_ad_bits(l1p + guest_l1_table_offset(va), &gw->l1e, 
+                                 (pfec & PFEC_write_access)) )
+                    paging_mark_dirty(d, mfn_x(gw->l1mfn));
+            }
         }
     }
 
diff -r 4f2c59fb28e6 -r 6d15152fb59a xen/include/asm-x86/guest_pt.h
--- a/xen/include/asm-x86/guest_pt.h
+++ b/xen/include/asm-x86/guest_pt.h
@@ -194,6 +194,17 @@ guest_supports_superpages(struct vcpu *v
 }
 
 static inline int
+guest_supports_1G_superpages(struct vcpu *v)
+{
+    if (!guest_supports_superpages(v))
+        return 0;
+
+    return (GUEST_PAGING_LEVELS >= 4
+           && hvm_pse1gb_supported(v->domain)
+           && hvm_long_mode_enabled(v));
+}
+
+static inline int
 guest_supports_nx(struct vcpu *v)
 {
     if ( GUEST_PAGING_LEVELS == 2 || !cpu_has_nx )
diff -r 4f2c59fb28e6 -r 6d15152fb59a xen/include/asm-x86/hvm/hvm.h
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -224,6 +224,9 @@ int hvm_girq_dest_2_vcpu_id(struct domai
 #define hvm_hap_has_2mb(d) \
     (hvm_funcs.hap_capabilities & HVM_HAP_SUPERPAGE_2MB)
 
+#define hvm_pse1gb_supported(d) \
+    (cpu_has_page1gb && hvm_hap_has_1gb(d) && paging_mode_hap(d))
+
 #ifdef __x86_64__
 #define hvm_long_mode_enabled(v) \
     ((v)->arch.hvm_vcpu.guest_efer & EFER_LMA)

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