Re: [PATCH v6 09/10] i386/pc: relocate 4g start to 1T where applicable

[Joao Martins]

On 7/11/22 13:56, Igor Mammedov wrote:
> On Fri,  1 Jul 2022 17:10:13 +0100
> Joao Martins <joao.m.martins@oracle.com> wrote:
> 
>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
>> index a79fa1b6beeb..07025b510540 100644
>> --- a/hw/i386/pc.c
>> +++ b/hw/i386/pc.c
>> @@ -907,6 +907,87 @@ static uint64_t pc_get_cxl_range_end(PCMachineState 
>> *pcms)
>>      return start;
>>  }
>>  
>> +static hwaddr pc_max_used_gpa(PCMachineState *pcms,
>> +                                hwaddr above_4g_mem_start,
>> +                                uint64_t pci_hole64_size)
>> +{
>> +    X86MachineState *x86ms = X86_MACHINE(pcms);
>> +
> 
>> +    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;
>> +    }
> this hunk still bothers me (nothing changed wrt v5 issues around it)
> issues recap: (
>  1. correctness of it
>  2. being limited to AMD only, while it seems pretty generic to me
>  3. should be a separate patch
> )
> 
How about I instead delete this hunk, and only call 
pc_set_amd_above_4g_mem_start()
when there's @above_4g_mem_size ? Like in pc_memory_init() I would instead:

if (IS_AMD_CPU(&cpu->env) && x86ms->above_4g_mem_size) {
    hwaddr start = x86ms->above_4g_mem_start;

    if (pc_max_used_gpa(pcms, start, pci_hole64_size) >= AMD_HT_START) {
        pc_set_amd_above_4g_mem_start(pcms, pci_hole64_size);
    }
    ...
}

Given that otherwise it is impossible to ever encounter the 1T boundary.

If not ... what other alternative would address your concern?

>> +
>> +    return pc_pci_hole64_start() + pci_hole64_size;
>> +}
>> +
>> +/*
>> + * AMD systems with an IOMMU have an additional hole close to the
>> + * 1Tb, which are special GPAs that cannot be DMA mapped. Depending
>> + * on kernel version, VFIO may or may not let you DMA map those ranges.
>> + * Starting Linux v5.4 we validate it, and can't create guests on AMD 
>> machines
>> + * with certain memory sizes. It's also wrong to use those IOVA ranges
>> + * in detriment of leading to IOMMU INVALID_DEVICE_REQUEST or worse.
>> + * The ranges reserved for Hyper-Transport are:
>> + *
>> + * FD_0000_0000h - FF_FFFF_FFFFh
>> + *
>> + * The ranges represent the following:
>> + *
>> + * Base Address   Top Address  Use
>> + *
>> + * FD_0000_0000h FD_F7FF_FFFFh Reserved interrupt address space
>> + * FD_F800_0000h FD_F8FF_FFFFh Interrupt/EOI IntCtl
>> + * FD_F900_0000h FD_F90F_FFFFh Legacy PIC IACK
>> + * FD_F910_0000h FD_F91F_FFFFh System Management
>> + * FD_F920_0000h FD_FAFF_FFFFh Reserved Page Tables
>> + * FD_FB00_0000h FD_FBFF_FFFFh Address Translation
>> + * FD_FC00_0000h FD_FDFF_FFFFh I/O Space
>> + * FD_FE00_0000h FD_FFFF_FFFFh Configuration
>> + * FE_0000_0000h FE_1FFF_FFFFh Extended Configuration/Device Messages
>> + * FE_2000_0000h FF_FFFF_FFFFh Reserved
>> + *
>> + * See AMD IOMMU spec, section 2.1.2 "IOMMU Logical Topology",
>> + * Table 3: Special Address Controls (GPA) for more information.
>> + */
>> +#define AMD_HT_START         0xfd00000000UL
>> +#define AMD_HT_END           0xffffffffffUL
>> +#define AMD_ABOVE_1TB_START  (AMD_HT_END + 1)
>> +#define AMD_HT_SIZE          (AMD_ABOVE_1TB_START - AMD_HT_START)
>> +
>> +static void pc_set_amd_above_4g_mem_start(PCMachineState *pcms,
>> +                                          uint64_t pci_hole64_size)
>> +{
>> +    X86MachineState *x86ms = X86_MACHINE(pcms);
>> +    hwaddr start = x86ms->above_4g_mem_start;
>> +    hwaddr maxphysaddr, maxusedaddr;
>> +
>> +    /* Bail out if max possible address does not cross HT range */
>> +    if (pc_max_used_gpa(pcms, start, pci_hole64_size) < AMD_HT_START) {
> 
> move it to the caller?
> 
Will do. I have replaced with this instead /in the caller/:

    if (pc_max_used_gpa(pcms, start, pci_hole64_size) >= AMD_HT_START) {
        pc_set_amd_above_4g_mem_start(pcms, pci_hole64_size);
    }

>> +        return;
>> +    }
>> +
>> +    /*
>> +     * Relocating ram-above-4G requires more than TCG_PHYS_ADDR_BITS (40).
>> +     * So make sure phys-bits is required to be appropriately sized in order
>> +     * to proceed with the above-4g-region relocation and thus boot.
>> +     */
>> +    start = AMD_ABOVE_1TB_START;
>> +    maxphysaddr = ((hwaddr)1 << X86_CPU(first_cpu)->phys_bits) - 1;
>> +    maxusedaddr = pc_max_used_gpa(pcms, start, pci_hole64_size);
>> +    if (maxphysaddr < maxusedaddr) {
>> +        error_report("Address space limit 0x%"PRIx64" < 0x%"PRIx64
>> +                     " phys-bits too low (%u) cannot avoid AMD HT range",
>> +                     maxphysaddr, maxusedaddr, 
>> X86_CPU(first_cpu)->phys_bits);
>> +        exit(EXIT_FAILURE);
>> +    }
>> +
>> +    x86ms->above_4g_mem_start = start;
>> +}
>> +
>>  void pc_memory_init(PCMachineState *pcms,
>>                      MemoryRegion *system_memory,
>>                      MemoryRegion *rom_memory,
>> @@ -922,12 +1003,31 @@ void pc_memory_init(PCMachineState *pcms,
>>      PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>>      X86MachineState *x86ms = X86_MACHINE(pcms);
>>      hwaddr cxl_base, cxl_resv_end = 0;
>> +    X86CPU *cpu = X86_CPU(first_cpu);
>>  
>>      assert(machine->ram_size == x86ms->below_4g_mem_size +
>>                                  x86ms->above_4g_mem_size);
>>  
>>      linux_boot = (machine->kernel_filename != NULL);
>>  
>> +    /*
>> +     * The HyperTransport range close to the 1T boundary is unique to AMD
>> +     * hosts with IOMMUs enabled. Restrict the ram-above-4g relocation
>> +     * to above 1T to AMD vCPUs only.
>> +     */
>> +    if (IS_AMD_CPU(&cpu->env)) {
>> +        pc_set_amd_above_4g_mem_start(pcms, pci_hole64_size);
>> +
>> +        /*
>> +         * Advertise the HT region if address space covers the reserved
>> +         * region or if we relocate.
>> +         */
>> +        if (x86ms->above_4g_mem_start == AMD_ABOVE_1TB_START ||
>> +            cpu->phys_bits >= 40) {
>> +            e820_add_entry(AMD_HT_START, AMD_HT_SIZE, E820_RESERVED);
>> +        }
>> +    }
>> +
>>      /*
>>       * Split single memory region and use aliases to address portions of it,
>>       * done for backwards compatibility with older qemus.
>> @@ -938,6 +1038,7 @@ void pc_memory_init(PCMachineState *pcms,
>>                               0, x86ms->below_4g_mem_size);
>>      memory_region_add_subregion(system_memory, 0, ram_below_4g);
>>      e820_add_entry(0, x86ms->below_4g_mem_size, E820_RAM);
>> +
> 
> stray newline?
> 
Yeap. I've already removed as per my earlier email to this patch.