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

[Igor Mammedov]

On Mon, 11 Jul 2022 21:03:28 +0100
Joao Martins <joao.m.martins@oracle.com> wrote:

> On 7/11/22 16:31, Joao Martins wrote:
> > On 7/11/22 15:52, Joao Martins wrote:  
> >> 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.
> >>  
> > 
> > And while at it I would also remove any unneeded arguments from 
> > pc_max_used_gpa(),
> > which would turn the function into this:
> > 
> > +static hwaddr pc_max_used_gpa(uint64_t pci_hole64_size)
> > +{
> > +    return pc_pci_hole64_start() + pci_hole64_size;
> > +}
> > 
> > I would nuke the added helper if it wasn't for having 2 call sites in this 
> > patch.
> >   
> 
> Full patch diff further below -- after removing pc_max_used_gpa() and made 
> further
> cleanups given this code can be much simpler after using this approach.
> 
> >> If not ... what other alternative would address your concern?
> >>  
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index e178bbc4129c..1ded3faeffe0 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -882,6 +882,62 @@ static uint64_t pc_get_cxl_range_end(PCMachineState 
> *pcms)
>      return start;
>  }
> 
> +/*
> + * 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,
> +                                          hwaddr maxusedaddr)
> +{
> +    X86MachineState *x86ms = X86_MACHINE(pcms);
> +    hwaddr maxphysaddr;
> +
> +    /*
> +     * 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.
> +     */
> +    maxphysaddr = ((hwaddr)1 << X86_CPU(first_cpu)->phys_bits) - 1;
> +    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 = AMD_ABOVE_1TB_START;
> +}
> +
>  void pc_memory_init(PCMachineState *pcms,
>                      MemoryRegion *system_memory,
>                      MemoryRegion *rom_memory,
> @@ -897,6 +953,7 @@ 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);
> @@ -904,6 +961,29 @@ void pc_memory_init(PCMachineState *pcms,
>      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) && x86ms->above_4g_mem_size) {

it has the same issue as pc_max_used_gpa(), i.e.
  x86ms->above_4g_mem_size != 0
doesn't mean that there isn't any memory above 4Gb nor that there aren't
any MMIO (sgx/cxl/pci64hole), that's was the reason we were are considering
max_used_gpa

I'd prefer to keep pc_max_used_gpa(),
idea but make it work for above cases and be more generic (i.e. not to be
tied to AMD only) since 'pc_max_used_gpa() < physbits' applies to equally
to AMD and Intel (and to trip it, one just have to configure small enough
physbits or large enough hotpluggable RAM/CXL/PCI64HOLE)



> +        hwaddr maxusedaddr = pc_pci_hole64_start() + pci_hole64_size;
> +
> +        /* Bail out if max possible address does not cross HT range */
> +        if (maxusedaddr >= AMD_HT_START) {
> +            pc_set_amd_above_4g_mem_start(pcms, maxusedaddr);
> +        }
> +
> +        /*
> +         * 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.
>       */
>