Re: [Xen-devel] [PATCH v2] nested VMX: don't ignore mapping errors

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

Acked by: Eddie Dong <eddie.dong@xxxxxxxxx>

-----Original Message-----
From: Jan Beulich [mailto:JBeulich@xxxxxxxx] 
Sent: Monday, November 11, 2013 7:07 PM
To: xen-devel
Cc: Andrew Cooper; Dong, Eddie; Nakajima, Jun
Subject: [PATCH v2] nested VMX: don't ignore mapping errors

Rather than ignoring failures to map the virtual VMCS as well as MSR or I/O 
port bitmaps, convert those into failures of the respective instructions 
(avoiding to dereference NULL pointers). Ultimately such failures should be 
handled transparently (by using transient mappings when they actually need to 
be accessed, just like nested SVM does).

Once at it, also eliminate a pointless (and incomplete) result check:
Non-global (i.e. non-permanent) map operations can't fail.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Remove the change to nvmx_handle_vmclear() -
    hvm_map_guest_frame_*() can return NULL for reasons other than
    map_domain_page_global() doing so (pointed out by Andrew Cooper).
    That leaves the function broken though (it ought to handle the
    shared/paged out cases in an appropriate way).

--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -747,7 +747,7 @@ static void __clear_current_vvmcs(struct
         __vmpclear(virt_to_maddr(nvcpu->nv_n2vmcx));
 }
 
-static void __map_msr_bitmap(struct vcpu *v)
+static bool_t __must_check _map_msr_bitmap(struct vcpu *v)
 {
     struct nestedvmx *nvmx = &vcpu_2_nvmx(v);
     unsigned long gpa;
@@ -756,9 +756,11 @@ static void __map_msr_bitmap(struct vcpu
         hvm_unmap_guest_frame(nvmx->msrbitmap, 1);
     gpa = __get_vvmcs(vcpu_nestedhvm(v).nv_vvmcx, MSR_BITMAP);
     nvmx->msrbitmap = hvm_map_guest_frame_ro(gpa >> PAGE_SHIFT, 1);
+
+    return nvmx->msrbitmap != NULL;
 }
 
-static void __map_io_bitmap(struct vcpu *v, u64 vmcs_reg)
+static bool_t __must_check _map_io_bitmap(struct vcpu *v, u64 vmcs_reg)
 {
     struct nestedvmx *nvmx = &vcpu_2_nvmx(v);
     unsigned long gpa;
@@ -769,12 +771,14 @@ static void __map_io_bitmap(struct vcpu 
         hvm_unmap_guest_frame(nvmx->iobitmap[index], 1);
     gpa = __get_vvmcs(vcpu_nestedhvm(v).nv_vvmcx, vmcs_reg);
     nvmx->iobitmap[index] = hvm_map_guest_frame_ro(gpa >> PAGE_SHIFT, 1);
+
+    return nvmx->iobitmap[index] != NULL;
 }
 
-static inline void map_io_bitmap_all(struct vcpu *v)
+static inline bool_t __must_check map_io_bitmap_all(struct vcpu *v)
 {
-   __map_io_bitmap (v, IO_BITMAP_A);
-   __map_io_bitmap (v, IO_BITMAP_B);
+   return _map_io_bitmap(v, IO_BITMAP_A) &&
+          _map_io_bitmap(v, IO_BITMAP_B);
 }
 
 static void nvmx_purge_vvmcs(struct vcpu *v) @@ -1610,9 +1614,15 @@ int 
nvmx_handle_vmptrld(struct cpu_user_
     if ( nvcpu->nv_vvmcxaddr == VMCX_EADDR )
     {
         nvcpu->nv_vvmcx = hvm_map_guest_frame_rw(gpa >> PAGE_SHIFT, 1);
-        nvcpu->nv_vvmcxaddr = gpa;
-        map_io_bitmap_all (v);
-        __map_msr_bitmap(v);
+        if ( nvcpu->nv_vvmcx )
+            nvcpu->nv_vvmcxaddr = gpa;
+        if ( !nvcpu->nv_vvmcx ||
+             !map_io_bitmap_all(v) ||
+             !_map_msr_bitmap(v) )
+        {
+            vmreturn(regs, VMFAIL_VALID);
+            goto out;
+        }
     }
 
     if ( cpu_has_vmx_vmcs_shadowing )
@@ -1724,6 +1734,7 @@ int nvmx_handle_vmwrite(struct cpu_user_
     struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v);
     unsigned long operand; 
     u64 vmcs_encoding;
+    bool_t okay = 1;
 
     if ( decode_vmx_inst(regs, &decode, &operand, 0)
              != X86EMUL_OKAY )
@@ -1732,16 +1743,21 @@ int nvmx_handle_vmwrite(struct cpu_user_
     vmcs_encoding = reg_read(regs, decode.reg2);
     __set_vvmcs(nvcpu->nv_vvmcx, vmcs_encoding, operand);
 
-    if ( vmcs_encoding == IO_BITMAP_A || vmcs_encoding == IO_BITMAP_A_HIGH )
-        __map_io_bitmap (v, IO_BITMAP_A);
-    else if ( vmcs_encoding == IO_BITMAP_B || 
-              vmcs_encoding == IO_BITMAP_B_HIGH )
-        __map_io_bitmap (v, IO_BITMAP_B);
+    switch ( vmcs_encoding )
+    {
+    case IO_BITMAP_A: case IO_BITMAP_A_HIGH:
+        okay = _map_io_bitmap(v, IO_BITMAP_A);
+        break;
+    case IO_BITMAP_B: case IO_BITMAP_B_HIGH:
+        okay = _map_io_bitmap(v, IO_BITMAP_B);
+        break;
+    case MSR_BITMAP: case MSR_BITMAP_HIGH:
+        okay = _map_msr_bitmap(v);
+        break;
+    }
 
-    if ( vmcs_encoding == MSR_BITMAP || vmcs_encoding == MSR_BITMAP_HIGH )
-        __map_msr_bitmap(v);
+    vmreturn(regs, okay ? VMSUCCEED : VMFAIL_VALID);
 
-    vmreturn(regs, VMSUCCEED);
     return X86EMUL_OKAY;
 }
 



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