Re: [PATCH v5 4/5] i386/pc: relocate 4g start to 1T where applicable

[Joao Martins]

On 6/28/22 13:38, Igor Mammedov wrote:
> On Mon, 20 Jun 2022 19:13:46 +0100
> Joao Martins <joao.m.martins@oracle.com> wrote:
> 
>> On 6/20/22 17:36, Joao Martins wrote:
>>> On 6/20/22 15:27, Igor Mammedov wrote:  
>>>> On Fri, 17 Jun 2022 14:33:02 +0100
>>>> Joao Martins <joao.m.martins@oracle.com> wrote:  
>>>>> On 6/17/22 13:32, Igor Mammedov wrote:  
>>>>>> On Fri, 17 Jun 2022 13:18:38 +0100
>>>>>> Joao Martins <joao.m.martins@oracle.com> wrote:    
>>>>>>> On 6/16/22 15:23, Igor Mammedov wrote:    
>>>>>>>> On Fri, 20 May 2022 11:45:31 +0100
>>>>>>>> Joao Martins <joao.m.martins@oracle.com> wrote:    
>>>>>>>>> +                                hwaddr above_4g_mem_start,
>>>>>>>>> +                                uint64_t pci_hole64_size)
>>>>>>>>> +{
>>>>>>>>> +    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>>>>>>>>> +    X86MachineState *x86ms = X86_MACHINE(pcms);
>>>>>>>>> +    MachineState *machine = MACHINE(pcms);
>>>>>>>>> +    ram_addr_t device_mem_size = 0;
>>>>>>>>> +    hwaddr base;
>>>>>>>>> +
>>>>>>>>> +    if (!x86ms->above_4g_mem_size) {
>>>>>>>>> +       /*
>>>>>>>>> +        * 32-bit pci hole goes from
>>>>>>>>> +        * end-of-low-ram (@below_4g_mem_size) to IOAPIC.
>>>>>>>>> +        */
>>>>>>>>> +        return IO_APIC_DEFAULT_ADDRESS - 1;      
>>>>>>>>
>>>>>>>> lack of above_4g_mem, doesn't mean absence of device_mem_size or 
>>>>>>>> anything else
>>>>>>>> that's located above it.
>>>>>>>>       
>>>>>>>
>>>>>>> True. But the intent is to fix 32-bit boundaries as one of the qtests 
>>>>>>> was failing
>>>>>>> otherwise. We won't hit the 1T hole, hence a nop.    
>>>>>>
>>>>>> I don't get the reasoning, can you clarify it pls?
>>>>>>     
>>>>>
>>>>> I was trying to say that what lead me here was a couple of qtests 
>>>>> failures (from v3->v4).
>>>>>
>>>>> I was doing this before based on pci_hole64. phys-bits=32 was for example 
>>>>> one
>>>>> of the test failures, and pci-hole64 sits above what 32-bit can 
>>>>> reference.  
>>>>
>>>> if user sets phys-bits=32, then nothing above 4Gb should work (be usable)
>>>> (including above-4g-ram, hotplug region or pci64 hole or sgx or cxl)
>>>>
>>>> and this doesn't look to me as AMD specific issue
>>>>
>>>> perhaps do a phys-bits check as a separate patch
>>>> that will error out if max_used_gpa is above phys-bits limit
>>>> (maybe at machine_done time)
>>>> (i.e. defining max_gpa and checking if compatible with configured cpu
>>>> are 2 different things)
>>>>
>>>> (it might be possible that tests need to be fixed too to account for it)
>>>>  
>>>
>>> My old notes (from v3) tell me with such a check these tests were exiting 
>>> early thanks to
>>> that error:
>>>
>>>  1/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/qom-test               ERROR   
>>>         0.07s
>>>   killed by signal 6 SIGABRT
>>>  4/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/test-hmp               ERROR   
>>>         0.07s
>>>   killed by signal 6 SIGABRT
>>>  7/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/boot-serial-test       ERROR   
>>>         0.07s
>>>   killed by signal 6 SIGABRT
>>> 44/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/test-x86-cpuid-compat  ERROR   
>>>         0.09s
>>>   killed by signal 6 SIGABRT
>>> 45/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/numa-test              ERROR   
>>>         0.17s
>>>   killed by signal 6 SIGABRT
>>>
>>> But the real reason these fail is not at all related to CPU phys bits,
>>> but because we just don't handle the case where no pci_hole64 is supposed 
>>> to exist (which
>>> is what that other check is trying to do) e.g. A VM with -m 1G would
>>> observe the same thing i.e. the computations after that conditional are all 
>>> for the pci
>>> hole64, which acounts for SGX/CXL/hotplug or etc which consequently means 
>>> it's *errousnly*
>>> bigger than phys-bits=32 (by definition). So the error_report is just 
>>> telling me that
>>> pc_max_used_gpa() is just incorrect without the !x86ms->above_4g_mem_size 
>>> check.
>>>
>>> If you're not fond of:
>>>
>>> +    if (!x86ms->above_4g_mem_size) {
>>> +       /*
>>> +        * 32-bit pci hole goes from
>>> +        * end-of-low-ram (@below_4g_mem_size) to IOAPIC.
>>> +         */
>>> +        return IO_APIC_DEFAULT_ADDRESS - 1;
>>> +    }
>>>
>>> Then what should I use instead of the above?
>>>
>>> 'IO_APIC_DEFAULT_ADDRESS - 1' is the size of the 32-bit PCI hole, which is
>>> also what is used for i440fx/q35 code. I could move it to a macro (e.g.
>>> PCI_HOST_HOLE32_SIZE) to make it a bit readable and less hardcoded. Or
>>> perhaps your problem is on !x86ms->above_4g_mem_size and maybe I should 
>>> check
>>> in addition for hotplug/CXL/etc existence?
>>>   
>>>>>>>  Unless we plan on using
>>>>>>> pc_max_used_gpa() for something else other than this.    
>>>>>>
>>>>>> Even if '!above_4g_mem_sizem', we can still have hotpluggable memory 
>>>>>> region
>>>>>> present and that can  hit 1Tb. The same goes for pci64_hole if it's 
>>>>>> configured
>>>>>> large enough on CLI.
>>>>>>     
>>>>> So hotpluggable memory seems to assume it sits above 4g mem.
>>>>>
>>>>> pci_hole64 likewise as it uses similar computations as hotplug.
>>>>>
>>>>> Unless I am misunderstanding something here.
>>>>>  
>>>>>> Looks like guesstimate we could use is taking pci64_hole_end as max used 
>>>>>> GPA
>>>>>>     
>>>>> I think this was what I had before (v3[0]) and did not work.  
>>>>
>>>> that had been tied to host's phys-bits directly, all in one patch
>>>> and duplicating existing pc_pci_hole64_start().
>>>>    
>>>
>>> Duplicating was sort of my bad attempt in this patch for pc_max_used_gpa()
>>>
>>> I was sort of thinking to something like extracting calls to start + size 
>>> "tuple" into
>>> functions -- e.g. for hotplug it is pc_get_device_memory_range() and for 
>>> CXL it would be
>>> maybe pc_get_cxl_range()) -- rather than assuming those values are already 
>>> initialized on
>>> the memory-region @base and its size.
>>>
>>> See snippet below. Note I am missing CXL handling, but gives you the idea.
>>>
>>> But it is slightly more complex than what I had in this version :( and 
>>> would require
>>> anyone doing changes in pc_memory_init() and pc_pci_hole64_start() to make 
>>> sure it follows
>>> the similar logic.
>>>   
>>
>> Ignore previous snippet, here's a slightly cleaner version:
> 
> lets go with this version
> 

OK. I have splited into 5 new patches:

578f551a41f0 i386/pc: handle unitialized mr in pc_get_cxl_range_end()
49256313cfd9 i386/pc: factor out cxl range start to helper
4bc1836bd588 i386/pc: factor out cxl range end to helper
e83cc9d3081c i386/pc: factor out device_memory base/size to helper
1ccb5064338e i386/pc: factor out above-4g end to an helper

Will re-test and respin the series.

The core of the series (in this patch) doesn't change and just gets simpler.

>>
>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
>> index 8eaa32ee2106..1d97c77a5eac 100644
>> --- a/hw/i386/pc.c
>> +++ b/hw/i386/pc.c
>> @@ -803,6 +803,43 @@ void xen_load_linux(PCMachineState *pcms)
>>  #define PC_ROM_ALIGN       0x800
>>  #define PC_ROM_SIZE        (PC_ROM_MAX - PC_ROM_MIN_VGA)
>>
>> +static void pc_get_device_memory_range(PCMachineState *pcms,
>> +                                       hwaddr *base,
>> +                                       hwaddr *device_mem_size)
>> +{
>> +    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>> +    X86MachineState *x86ms = X86_MACHINE(pcms);
>> +    MachineState *machine = MACHINE(pcms);
>> +    hwaddr addr, size;
>> +
>> +    if (pcmc->has_reserved_memory &&
>> +        machine->device_memory && machine->device_memory->base) {
>> +        addr = machine->device_memory->base;
>> +        size = memory_region_size(&machine->device_memory->mr);
>> +        goto out;
>> +    }
>> +
>> +    /* uninitialized memory region */
>> +    size = machine->maxram_size - machine->ram_size;
>> +
>> +    if (pcms->sgx_epc.size != 0) {
>> +        addr = sgx_epc_above_4g_end(&pcms->sgx_epc);
>> +    } else {
>> +        addr = x86ms->above_4g_mem_start + x86ms->above_4g_mem_size;
>> +    }
>> +
>> +    if (pcmc->enforce_aligned_dimm) {
>> +        /* size device region assuming 1G page max alignment per slot */
>> +        size += (1 * GiB) * machine->ram_slots;
>> +    }
>> +
>> +out:
>> +    if (base)
>> +        *base = addr;
>> +    if (device_mem_size)
>> +        *device_mem_size = size;
>> +}
>> +
>>  void pc_memory_init(PCMachineState *pcms,
>>                      MemoryRegion *system_memory,
>>                      MemoryRegion *rom_memory,
>> @@ -864,7 +901,7 @@ void pc_memory_init(PCMachineState *pcms,
>>      /* initialize device memory address space */
>>      if (pcmc->has_reserved_memory &&
>>          (machine->ram_size < machine->maxram_size)) {
>> -        ram_addr_t device_mem_size = machine->maxram_size - 
>> machine->ram_size;
>> +        ram_addr_t device_mem_size;
>>
>>          if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
>>              error_report("unsupported amount of memory slots: %"PRIu64,
>> @@ -879,20 +916,7 @@ void pc_memory_init(PCMachineState *pcms,
>>              exit(EXIT_FAILURE);
>>          }
>>
>> -        if (pcms->sgx_epc.size != 0) {
>> -            machine->device_memory->base = 
>> sgx_epc_above_4g_end(&pcms->sgx_epc);
>> -        } else {
>> -            machine->device_memory->base =
>> -                x86ms->above_4g_mem_start + x86ms->above_4g_mem_size;
>> -        }
>> -
>> -        machine->device_memory->base =
>> -            ROUND_UP(machine->device_memory->base, 1 * GiB);
>> -
>> -        if (pcmc->enforce_aligned_dimm) {
>> -            /* size device region assuming 1G page max alignment per slot */
>> -            device_mem_size += (1 * GiB) * machine->ram_slots;
>> -        }
>> +        pc_get_device_memory_range(pcms, &machine->device_memory->base, 
>> &device_mem_size);
>>
>>          if ((machine->device_memory->base + device_mem_size) <
>>              device_mem_size) {
>> @@ -965,12 +989,13 @@ uint64_t pc_pci_hole64_start(void)
>>      PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>>      MachineState *ms = MACHINE(pcms);
>>      X86MachineState *x86ms = X86_MACHINE(pcms);
>> -    uint64_t hole64_start = 0;
>> +    uint64_t hole64_start = 0, size = 0;
>>
>> -    if (pcmc->has_reserved_memory && ms->device_memory->base) {
>> -        hole64_start = ms->device_memory->base;
>> +    if (pcmc->has_reserved_memory &&
>> +        (ms->ram_size < ms->maxram_size)) {
>> +        pc_get_device_memory_range(pcms, &hole64_start, &size);
>>          if (!pcmc->broken_reserved_end) {
>> -            hole64_start += memory_region_size(&ms->device_memory->mr);
>> +            hole64_start += size;
>>          }
>>      } else if (pcms->sgx_epc.size != 0) {
>>              hole64_start = sgx_epc_above_4g_end(&pcms->sgx_epc);
>>
>