Re: [PATCH v3 3/8] acpi/gpex: Inform os to keep firmware resource map

[Laszlo Ersek <lersek@redhat.com>]

On 01/05/21 01:35, Igor Mammedov wrote:
> On Wed, 30 Dec 2020 16:22:08 -0500
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
>> On Tue, Dec 29, 2020 at 02:41:42PM +0100, Igor Mammedov wrote:
>>> On Wed, 23 Dec 2020 17:08:31 +0800
>>> Jiahui Cen <cenjiahui@huawei.com> wrote:
>>>   
>>>> There may be some differences in pci resource assignment between guest os
>>>> and firmware.
>>>>
>>>> Eg. A Bridge with Bus [d2]
>>>>     -+-[0000:d2]---01.0-[d3]----01.0
>>>>
>>>>     where [d2:01.00] is a pcie-pci-bridge with BAR0 (mem, 64-bit, non-pref) [size=256]
>>>>           [d3:01.00] is a PCI Device with BAR0 (mem, 64-bit, pref) [size=128K]
>>>>                                           BAR4 (mem, 64-bit, pref) [size=64M]
>>>>
>>>>     In EDK2, the Resource Map would be:
>>>>         PciBus: Resource Map for Bridge [D2|01|00]
>>>>         Type = PMem64; Base = 0x8004000000;     Length = 0x4100000;     Alignment = 0x3FFFFFF
>>>>            Base = 0x8004000000; Length = 0x4000000;     Alignment = 0x3FFFFFF;  Owner = PCI [D3|01|00:20]
>>>>            Base = 0x8008000000; Length = 0x20000;       Alignment = 0x1FFFF;    Owner = PCI [D3|01|00:10]
>>>>         Type =  Mem64; Base = 0x8008100000;     Length = 0x100; Alignment = 0xFFF
>>>>     It would use 0x4100000 to calculate the root bus's PMem64 resource window.
>>>>
>>>>     While in Linux, kernel will use 0x1FFFFFF as the alignment to calculate
>>>>     the PMem64 size, which would be 0x6000000. So kernel would try to
>>>>     allocate 0x6000000 from the PMem64 resource window, but since the window
>>>>     size is 0x4100000 as assigned by EDK2, the allocation would fail.
>>>>
>>>> The diffences could result in resource assignment failure.
>>>>
>>>> Using _DSM #5 method to inform guest os not to ignore the PCI configuration
>>>> that firmware has done at boot time could handle the differences.  
>>>
>>> I'm not sure about this one, 
>>> OS should able to reconfigure PCI resources according to what and where is plugged
>>> (and it even more true is hotplug is taken into account)  
>>
>> spec says this:
>>
>> 0: No (The operating system must not ignore the PCI configuration that firmware has done
>> at boot time. However, the operating system is free to configure the devices in this hierarchy
>> that have not been configured by the firmware. There may be a reduced level of hot plug
>> capability support in this hierarchy due to resource constraints. This situation is the same as
>> the legacy situation where this _DSM is not provided.)
>> 1: Yes (The operating system may ignore the PCI configuration that the firmware has done
>> at boot time, and reconfigure/rebalance the resources in the hierarchy.)
> I sort of convinced my self that's is just hotplug work might need to implement reconfiguration
> in guest kernel and maybe QEMU
> 
> Though I have a question,
> 
>  1. does it work for PC machine with current kernel, if so why?
>  2. what it would take to make it work for arm/virt?

The Linux/arm64 guest deals with PCI resources differently for
historical reasons. I was extremely confused by that as well, but Ard
explained here:
<https://www.redhat.com/archives/edk2-devel-archive/2020-December/msg01027.html>.

(Do not be alarmed by Ard's initial statement "That is not going to
work"; he later revised that here:
<https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg05033.html>.)

Thanks,
Laszlo

> 
>> and
>>
>> IMPLEMENTATION NOTE
>> This _DSM function provides backwards compatibility on platforms that can run legacy operating
>> systems.
>> Operating systems for two different architectures (e.g., x86 and x64) can be installed on a platform.
>> The firmware cannot distinguish the operating system in time to change the boot configuration of
>> devices. Say for instance, an x86 operating system in non-PAE mode is installed on a system. The
>> x86 operating system cannot access device resource space above 4 GiB. So the firmware is required
>> to configure devices at boot time using addresses below 4 GiB. On the other hand, if an x64
>> operating system is installed on this system, it can access device resources above the 4 GiB so it does
>> not want the firmware to constrain the resource assignment below 4 GiB that the firmware
>> configures at boot time. It is not possible for the firmware to change this by the time it boots the
>> operating system. Ignoring the configurations done by firmware at boot time will allow the
>> operating system to push resource assignment using addresses above 4 GiB for an x64 operating
>> system while constrain it to addresses below 4 GiB for an x86 operating system.
>>
>> so fundamentally, saying "1" here just means "you can ignore what
>> firmware configured if you like".
>>
>>
>> I have a different question though: our CRS etc is based on what
>> firmware configured. Is that ok? Or is ACPI expected to somehow
>> reconfigure itself when OS reconfigures devices?
>> Think it's ok but could not find documentation either way.
> 
> guest consume DSDT only at boot time,
> reconfiguration can done later by PCI subsystem without
> ACPI (at least it used to be so).
> 
> However DSM is dynamic,
> and maybe evaluated at runtime,
> though I don't know if kernel would re-evaluate this feature bit after boot
> 
> 
>>
>>
>>>>
>>>> Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
>>>> ---
>>>>  hw/pci-host/gpex-acpi.c | 18 ++++++++++++++++--
>>>>  1 file changed, 16 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/hw/pci-host/gpex-acpi.c b/hw/pci-host/gpex-acpi.c
>>>> index 11b3db8f71..c189306599 100644
>>>> --- a/hw/pci-host/gpex-acpi.c
>>>> +++ b/hw/pci-host/gpex-acpi.c
>>>> @@ -112,10 +112,24 @@ static void acpi_dsdt_add_pci_osc(Aml *dev)
>>>>      UUID = aml_touuid("E5C937D0-3553-4D7A-9117-EA4D19C3434D");
>>>>      ifctx = aml_if(aml_equal(aml_arg(0), UUID));
>>>>      ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(0)));
>>>> -    uint8_t byte_list[1] = {1};
>>>> -    buf = aml_buffer(1, byte_list);
>>>> +    uint8_t byte_list[] = {
>>>> +                0x1 << 0 /* support for functions other than function 0 */ |
>>>> +                0x1 << 5 /* support for function 5 */
>>>> +                };
>>>> +    buf = aml_buffer(ARRAY_SIZE(byte_list), byte_list);
>>>>      aml_append(ifctx1, aml_return(buf));
>>>>      aml_append(ifctx, ifctx1);
>>>> +
>>>> +    /* PCI Firmware Specification 3.1
>>>> +     * 4.6.5. _DSM for Ignoring PCI Boot Configurations
>>>> +     */
>>>> +    /* Arg2: Function Index: 5 */
>>>> +    ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(5)));
>>>> +    /* 0 - The operating system must not ignore the PCI configuration that
>>>> +     *     firmware has done at boot time.
>>>> +     */
>>>> +    aml_append(ifctx1, aml_return(aml_int(0)));
>>>> +    aml_append(ifctx, ifctx1);
>>>>      aml_append(method, ifctx);
>>>>  
>>>>      byte_list[0] = 0;  
>>
>>
> 
>