Re: [Qemu-devel] [PATCH v7 25/35] nvdimm acpi: init the resource used by NVDIMM ACPI

[Igor Mammedov]

On Thu, 5 Nov 2015 21:33:39 +0800
Xiao Guangrong <address@hidden> wrote:

> 
> 
> On 11/05/2015 09:03 PM, Igor Mammedov wrote:
> > On Thu, 5 Nov 2015 18:15:31 +0800
> > Xiao Guangrong <address@hidden> wrote:
> >
> >>
> >>
> >> On 11/05/2015 05:58 PM, Igor Mammedov wrote:
> >>> On Mon,  2 Nov 2015 17:13:27 +0800
> >>> Xiao Guangrong <address@hidden> wrote:
> >>>
> >>>> A page staring from 0xFF00000 and IO port 0x0a18 - 0xa1b in guest are
> >>>                                  ^^ missing one 0???
> >>>
> >>>> reserved for NVDIMM ACPI emulation, refer to docs/specs/acpi_nvdimm.txt
> >>>> for detailed design
> >>>>
> >>>> A parameter, 'nvdimm-support', is introduced for PIIX4_PM and ICH9-LPC
> >>>> that controls if nvdimm support is enabled, it is true on default and
> >>>> it is false on 2.4 and its earlier version to keep compatibility
> >>>>
> >>>> Signed-off-by: Xiao Guangrong <address@hidden>
> >>> [...]
> >>>
> >>>> @@ -33,6 +33,15 @@
> >>>>     */
> >>>>    #define MIN_NAMESPACE_LABEL_SIZE      (128UL << 10)
> >>>>
> >>>> +/*
> >>>> + * A page staring from 0xFF00000 and IO port 0x0a18 - 0xa1b in guest are
> >>>                                    ^^^ missing 0 or value in define below 
> >>> has an extra 0
> >>>
> >>>> + * reserved for NVDIMM ACPI emulation, refer to 
> >>>> docs/specs/acpi_nvdimm.txt
> >>>> + * for detailed design.
> >>>> + */
> >>>> +#define NVDIMM_ACPI_MEM_BASE          0xFF000000ULL
> >>> it still maps RAM at arbitrary place,
> >>> that's the reason why VMGenID patches hasn't been merged for
> >>> more than several months.
> >>> I'm not against of using (more exactly I'm for it) direct mapping
> >>> but we should reach consensus when and how to use it first.
> >>>
> >>> I'd wouldn't use addresses below 4G as it may be used firmware or
> >>> legacy hardware and I won't bet that 0xFF000000ULL won't conflict
> >>> with anything.
> >>> An alternative place to allocate reserve from could be high memory.
> >>> For pc we have "reserved-memory-end" which currently makes sure
> >>> that hotpluggable memory range isn't used by firmware.
> >>>
> >>> How about making API that allows to map additional memory
> >>> ranges before reserved-memory-end and pushes it up as mappings are
> >>> added.
> >>
> >> That what i did in the v1/v2 versions, however, as you noticed, using 
> >> 64-bit
> >> address in ACPI in QEMU is not a easy work - we can not simply make
> >> SSDT.rev = 2 to apply 64 bit address, the reason i have documented in
> >> v3's changelog:
> >>
> >>     3) we figure out a unused memory hole below 4G that is 0xFF00000 ~
> >>        0xFFF00000, this range is large enough for NVDIMM ACPI as build 
> >> 64-bit
> >>        ACPI SSDT/DSDT table will break windows XP.
> >>        BTW, only make SSDT.rev = 2 can not work since the width is only 
> >> depended
> >>        on DSDT.rev based on 19.6.28 DefinitionBlock (Declare Definition 
> >> Block)
> >>        in ACPI spec:
> >> | Note: For compatibility with ACPI versions before ACPI 2.0, the bit
> >> | width of Integer objects is dependent on the ComplianceRevision of the 
> >> DSDT.
> >> | If the ComplianceRevision is less than 2, all integers are restricted to 
> >> 32
> >> | bits. Otherwise, full 64-bit integers are used. The version of the DSDT 
> >> sets
> >> | the global integer width for all integers, including integers in SSDTs.
> >>     4) use the lowest ACPI spec version to document AML terms.
> >>
> >> The only way introducing 64 bit address is adding XSDT support that what
> >> Michael did before, however, it seems it need great efforts to do it as
> >> it will break OVMF. It's a long term workload. :(
> > to enable 64-bit integers in AML it's sufficient to change DSDT revision to 
> > 2,
> > I already have a patch that switches DSDT/SSDT to rev2.
> > Tests show it doesn't break WindowsXP (which is rev1) and uses 64-bit 
> > integers
> > on linux & later Windows versions.
> 
> Great, i remembered i did the similar test (directly change DSDT to rev2) and 
> it
> caused winXP blue screen. Could you please tell me where i can find your 
> patch?
https://github.com/imammedo/qemu/commits/mhpt_table_v2
following changes revision:
 pc: acpi: bump DSDT/SSDT compliance revision to v2
and here is user:
 acpi: memhp: simplify MCRS() using 64-bit math

when writing ASL one shall make sure that only XP supported
features are in global scope, which is evaluated when tables
are loaded and features of rev2 and higher are inside methods.
That way XP doesn't crash as far as it doesn't evaluate unsupported
opcode and one can guard those opcodes checking _REV object if neccesary.


> >>
> >> The luck thing is, the ACPI part is not ABI, we can move it to the high
> >> memory if QEMU supports XSDT is ready in future development.
> > But mapped control region is ABI and we can't change it if we find out later
> > that it breaks something.
> 
> But the ACPI code is completely built by QEMU, which is transparent to guest
> and guest should not depend on it, no?
unfortunately no, think about cross-version migration.