Re: [PATCH RFCv2 2/4] i386/pc: relocate 4g start to 1T where applicable

[Igor Mammedov]

On Mon,  7 Feb 2022 20:24:20 +0000
Joao Martins <joao.m.martins@oracle.com> wrote:

> It is assumed that the whole GPA space is available to be DMA
> addressable, within a given address space limit, expect for a
> tiny region before the 4G. Since Linux v5.4, VFIO validates
> whether the selected GPA is indeed valid i.e. not reserved by
> IOMMU on behalf of some specific devices or platform-defined
> restrictions, and thus failing the ioctl(VFIO_DMA_MAP) with
>  -EINVAL.
> 
> AMD systems with an IOMMU are examples of such platforms and
> particularly may only have these ranges as allowed:
> 
>       0000000000000000 - 00000000fedfffff (0      .. 3.982G)
>       00000000fef00000 - 000000fcffffffff (3.983G .. 1011.9G)
>       0000010000000000 - ffffffffffffffff (1Tb    .. 16Pb[*])
> 
> We already account for the 4G hole, albeit if the guest is big
> enough we will fail to allocate a guest with  >1010G due to the
> ~12G hole at the 1Tb boundary, reserved for HyperTransport (HT).
> 
> [*] there is another reserved region unrelated to HT that exists
> in the 256T boundaru in Fam 17h according to Errata #1286,
> documeted also in "Open-Source Register Reference for AMD Family
> 17h Processors (PUB)"
> 
> When creating the region above 4G, take into account that on AMD
> platforms the HyperTransport range is reserved and hence it
> cannot be used either as GPAs. On those cases rather than
> establishing the start of ram-above-4g to be 4G, relocate instead
> to 1Tb. See AMD IOMMU spec, section 2.1.2 "IOMMU Logical
> Topology", for more information on the underlying restriction of
> IOVAs.
> 
> After accounting for the 1Tb hole on AMD hosts, mtree should
> look like:
> 
> 0000000000000000-000000007fffffff (prio 0, i/o):
>        alias ram-below-4g @pc.ram 0000000000000000-000000007fffffff
> 0000010000000000-000001ff7fffffff (prio 0, i/o):
>       alias ram-above-4g @pc.ram 0000000080000000-000000ffffffffff
> 
> If the relocation is done, we also add the the reserved HT
> e820 range as reserved.
> 
> Suggested-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  hw/i386/pc.c      | 66 +++++++++++++++++++++++++++++++++++++++++++++++
>  target/i386/cpu.h |  4 +++
>  2 files changed, 70 insertions(+)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 7de0e87f4a3f..b060aedd38f3 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -802,6 +802,65 @@ void xen_load_linux(PCMachineState *pcms)
>  #define PC_ROM_ALIGN       0x800
>  #define PC_ROM_SIZE        (PC_ROM_MAX - PC_ROM_MIN_VGA)
>  
> +/*
> + * 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 relocate_4g(MachineState *machine, PCMachineState *pcms)

perhaps rename it to x86_update_above_4g_mem_start() ?


> +{
> +    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
> +    X86MachineState *x86ms = X86_MACHINE(pcms);
> +    ram_addr_t device_mem_size = 0;
> +    uint32_t eax, vendor[3];
> +
> +    host_cpuid(0x0, 0, &eax, &vendor[0], &vendor[2], &vendor[1]);
> +    if (!IS_AMD_VENDOR(vendor)) {
> +        return;
> +    }
> +
> +    if (pcmc->has_reserved_memory &&
> +       (machine->ram_size < machine->maxram_size)) {
> +        device_mem_size = machine->maxram_size - machine->ram_size;
> +    }
> +
> +    if ((x86ms->above_4g_mem_start + x86ms->above_4g_mem_size +
> +         device_mem_size) < AMD_HT_START) {
should it account for sgx as well?

what if above sum ends up right before AMD_HT_START,
and exit without adjusting above_4g_mem_start, but
pci64 hole eventually will fall into HT range?
Is it expected behaviour?

> +        return;
> +    }
> +
> +    x86ms->above_4g_mem_start = AMD_ABOVE_1TB_START;
> +}
> +
>  void pc_memory_init(PCMachineState *pcms,
>                      MemoryRegion *system_memory,
>                      MemoryRegion *rom_memory,
> @@ -821,6 +880,8 @@ void pc_memory_init(PCMachineState *pcms,
>  
>      linux_boot = (machine->kernel_filename != NULL);
>  
> +    relocate_4g(machine, pcms);
> +
>      /*
>       * Split single memory region and use aliases to address portions of it,
>       * done for backwards compatibility with older qemus.
> @@ -831,6 +892,11 @@ 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);
> +
> +    if (x86ms->above_4g_mem_start == AMD_ABOVE_1TB_START) {
> +        e820_add_entry(AMD_HT_START, AMD_HT_SIZE, E820_RESERVED);
> +    }

btw: do we have to add reservation record for HT zone, why?

>      if (x86ms->above_4g_mem_size > 0) {
>          ram_above_4g = g_malloc(sizeof(*ram_above_4g));
>          memory_region_init_alias(ram_above_4g, NULL, "ram-above-4g",
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 9911d7c8711b..1acebc569b02 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -906,6 +906,10 @@ typedef uint64_t FeatureWordArray[FEATURE_WORDS];
>  #define IS_AMD_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_AMD_1 && \
>                           (env)->cpuid_vendor2 == CPUID_VENDOR_AMD_2 && \
>                           (env)->cpuid_vendor3 == CPUID_VENDOR_AMD_3)
> +#define IS_AMD_VENDOR(vendor) ((vendor[0]) == CPUID_VENDOR_AMD_1 && \
> +                         (vendor[1]) == CPUID_VENDOR_AMD_2 && \
> +                         (vendor[2]) == CPUID_VENDOR_AMD_3)
> +
>  
>  #define CPUID_MWAIT_IBE     (1U << 1) /* Interrupts can exit capability */
>  #define CPUID_MWAIT_EMX     (1U << 0) /* enumeration supported */