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memory_manager: Fix address range calculation in MemorySlot

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The MCRS method returns a 64-bit memory range descriptor. The
calculation is supposed to be done as follows:

max = min + len - 1

However, every operand is represented not as a QWORD but as combination
of two DWORDs for high and low part. Till now, the calculation was done
this way, please see also inline comments:

max.lo = min.lo + len.lo //this may overflow, need to carry over to high
max.hi = min.hi + len.hi
max.hi = max.hi - 1 // subtraction needs to happen on the low part

This calculation has been corrected the following way:

max.lo = min.lo + len.lo
max.hi = min.hi + len.hi + (max.lo < min.lo) // check for overflow
max.lo = max.lo - 1 // subtract from low part

The relevant part from the generated ASL for the MCRS method:
```
Method (MCRS, 1, Serialized)
{
    Acquire (MLCK, 0xFFFF)
    \_SB.MHPC.MSEL = Arg0
    Name (MR64, ResourceTemplate ()
    {
	QWordMemory (ResourceProducer, PosDecode, MinFixed, MaxFixed, Cacheable, ReadWrite,
	    0x0000000000000000, // Granularity
	    0x0000000000000000, // Range Minimum
	    0xFFFFFFFFFFFFFFFE, // Range Maximum
	    0x0000000000000000, // Translation Offset
	    0xFFFFFFFFFFFFFFFF, // Length
	    ,, _Y00, AddressRangeMemory, TypeStatic)
    })
    CreateQWordField (MR64, \_SB.MHPC.MCRS._Y00._MIN, MINL)  // _MIN: Minimum Base Address
    CreateDWordField (MR64, 0x12, MINH)
    CreateQWordField (MR64, \_SB.MHPC.MCRS._Y00._MAX, MAXL)  // _MAX: Maximum Base Address
    CreateDWordField (MR64, 0x1A, MAXH)
    CreateQWordField (MR64, \_SB.MHPC.MCRS._Y00._LEN, LENL)  // _LEN: Length
    CreateDWordField (MR64, 0x2A, LENH)
    MINL = \_SB.MHPC.MHBL
    MINH = \_SB.MHPC.MHBH
    LENL = \_SB.MHPC.MHLL
    LENH = \_SB.MHPC.MHLH
    MAXL = (MINL + LENL) /* \_SB_.MHPC.MCRS.LENL */
    MAXH = (MINH + LENH) /* \_SB_.MHPC.MCRS.LENH */
    If ((MAXL < MINL))
    {
	MAXH += One /* \_SB_.MHPC.MCRS.MAXH */
    }

    MAXL -= One
    Release (MLCK)
    Return (MR64) /* \_SB_.MHPC.MCRS.MR64 */
}
```

Fixes #1800.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
This commit is contained in:
Anatol Belski
2021-04-08 20:05:38 +02:00
committed by Samuel Ortiz
parent 37e2784299
commit e1cc702327
3 changed files with 116 additions and 2 deletions
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docs/windows.md
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@@ -188,6 +188,8 @@ This allows for SSH login from a remote machine, for example through the `admini
CPU hotplug is supported. The VM operating system needs to support hotplug and be appropriately licensed. SKU limitations like constraints on the number of cores are to be taken into consideration. Note, that Windows doesn't support CPU hot-remove. When `ch-remote` is invoked to reduce the number of CPUs, the result will be visible after the OS reboot within the same hypervisor instance.
RAM hotplug is supported. Note, that while the `pnpmem.sys` driver in use supports RAM hot-remove, the RAM being unplugged has to be not in use and have no reserved pages. In most cases it means, hot-remove won't work. Same as with the CPU hot-remove, when `ch-remote` is invoked to reduce the RAM size, the result will be visible after the OS reboot.
## Debugging
The Windows guest debugging process relies heavily on QEMU and [socat](http://www.dest-unreach.org/socat/). The procedure requires two Windows VMs: