Re: [PATCH v3 4/6] i386/pc: relocate 4g start to 1T where applicable

[Joao Martins]

On 2/23/22 18:44, Joao Martins wrote:
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 360f4e10001b..6e4f5c87a2e5 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -802,6 +802,78 @@ 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 hwaddr x86_max_phys_addr(PCMachineState *pcms,
> +                                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;
> +

I am adding this extra check for 32-bit coverage (phys-bits=32)

+    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;
+    }