>>> I don't know the heritage of that code. I expect someone
>>> decided it was
>>> good enough to be getting on with but maybe now it is time
>to revisit
>>> and see if we can implement a watertight version which
>correctly uses
>>> hidden segment descriptor state which is readily available
>>> when running
>>> on VMX.
>>
>> My patch just enhanced the current implementation, and actually it
>> breaks windows, but I have a updated version in hand, and tests show
>> that all the combinations is OK till now.
>>
>> In my mind, the correct way is to identify whether a cpu is
>in big real
>> mode, but seems this is a little bit hard to do.
>
>Well, it's impossible to know for certain without looking at hidden
>descriptor state isn't it. Big real mode is only possible because the
>hidden state can be out of sync with the current execution mode.
>
>If that state can be made available to the address() function
>then it's
>implementation, and confidence in its correctness, becomes trivial. Do
>we have that state available directly in the guest at that point? Or
>would we need to grab the state from Xen?
>
Keir, do you think this one seems better?
When in real mode, we should always calculate address as ((seg & 0xFFFF)
<< 4) + off, big real mode obey the same rule.
When in real mode to protected mode transition, only the IP address
calculation should use real mode addressing.
-Xin
@@ -50,23 +50,42 @@ static char *rnames[] = { "ax", "cx", "d
static char *rnames[] = { "ax", "cx", "dx", "bx", "sp", "bp", "si",
"di" };
#endif /* DEBUG */
-unsigned
+static unsigned
address(struct regs *regs, unsigned seg, unsigned off)
{
unsigned long long entry;
- unsigned addr;
+ unsigned seg_base, seg_limit;
+ unsigned entry_low, entry_high;
if (seg == 0)
- return off;
-
- if (seg > oldctx.gdtr_limit)
+ {
+ if (mode == VM86_REAL || mode == VM86_REAL_TO_PROTECTED)
+ return off;
+ else
+ panic("segment is zero, but not in real
mode!\n");
+ }
+
+ if (mode == VM86_REAL || seg > oldctx.gdtr_limit ||
+ (mode == VM86_REAL_TO_PROTECTED && regs->cs == seg))
return ((seg & 0xFFFF) << 4) + off;
entry = ((unsigned long long *) oldctx.gdtr_base)[seg >> 3];
- addr = (((entry >> (56-24)) & 0xFF000000) |
- ((entry >> (32-16)) & 0x00FF0000) |
- ((entry >> ( 16)) & 0x0000FFFF)) + off;
- return addr;
+ entry_high = entry >> 32;
+ entry_low = entry & 0xFFFFFFFF;
+
+ seg_base = (entry_high & 0xFF000000) | ((entry >> 16) &
0xFFFFFF);
+ seg_limit = (entry_high & 0xF0000) | (entry_low & 0xFFFF);
+
+ if (entry_high & 0x8000 &&
+ ((entry_high & 0x800000 && off >> 12 <= seg_limit) ||
+ (!(entry_high & 0x800000) && off <= seg_limit)))
+ return seg_base + off;
+
+ panic("should never reach here in function address():\n\t"
+ "entry=0x%08x%08x, mode=%d, seg=0x%08x, offset=0x%08x\n",
+ entry_high, entry_low, mode, seg, off);
+
+ return 0;
}
#ifdef DEBUG
fix_vmxassist..1.patch
Description: fix_vmxassist..1.patch
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