Re: [Qemu-devel] [patch 2/2] i386: pc: align gpa<->hpa on 1GB boundary

[Paolo Bonzini <pbonzini@redhat.com>]

Il 24/10/2013 22:12, Marcelo Tosatti ha scritto:
> Align guest physical address and host physical address
> beyond guest 4GB on a 1GB boundary, in case hugetlbfs is used.
> 
> Otherwise 1GB TLBs cannot be cached for the range.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Index: qemu/hw/i386/pc.c
> ===================================================================
> --- qemu.orig/hw/i386/pc.c
> +++ qemu/hw/i386/pc.c
> @@ -1116,8 +1116,9 @@ FWCfgState *pc_memory_init(MemoryRegion
>  {
>      int linux_boot, i;
>      MemoryRegion *ram, *option_rom_mr;
> -    MemoryRegion *ram_below_4g, *ram_above_4g;
> +    MemoryRegion *ram_below_4g, *ram_above_4g, *ram_above_4g_piecetwo;
>      FWCfgState *fw_cfg;
> +    unsigned long hpagesize;
>  
>      linux_boot = (kernel_filename != NULL);
>  
> @@ -1129,6 +1130,7 @@ FWCfgState *pc_memory_init(MemoryRegion
>      memory_region_init_ram(ram, NULL, "pc.ram",
>                             below_4g_mem_size + above_4g_mem_size);
>      vmstate_register_ram_global(ram);
> +    hpagesize = qemu_get_ram_hpagesize(ram->ram_addr);
>      *ram_memory = ram;
>      ram_below_4g = g_malloc(sizeof(*ram_below_4g));
>      memory_region_init_alias(ram_below_4g, NULL, "ram-below-4g", ram,
> @@ -1136,10 +1138,46 @@ FWCfgState *pc_memory_init(MemoryRegion
>      memory_region_add_subregion(system_memory, 0, ram_below_4g);
>      if (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", ram,
> -                                 below_4g_mem_size, above_4g_mem_size);
> -        memory_region_add_subregion(system_memory, 0x100000000ULL,
> +
> +        /*
> +         *
> +         * If 1GB hugepages are used to back guest RAM, map guest address
> +         * space in the range [ramsize,ramsize+holesize] to the ram block
> +         * range [holestart, 4GB]
> +         *
> +         *                      0      h     4G     [ramsize,ramsize+holesize]
> +         *
> +         * guest-addr-space     [      ]     [      ][xxx]
> +         *                                /----------/
> +         * contiguous-ram-block [      ][xxx][     ]
> +         *
> +         * So that memory beyond 4GB is aligned on a 1GB boundary,
> +         * at the host physical address space.
> +         *
> +         */
> +        if (hpagesize == (1<<30)) {
> +            unsigned long holesize = 0x100000000ULL - below_4g_mem_size;
> +
> +            memory_region_init_alias(ram_above_4g, NULL, "ram-above-4g", ram,
> +                                    0x100000000ULL,
> +                                    above_4g_mem_size - holesize);
> +            memory_region_add_subregion(system_memory, 0x100000000ULL,
> +                                    ram_above_4g);
> +
> +            ram_above_4g_piecetwo = g_malloc(sizeof(*ram_above_4g_piecetwo));
> +            memory_region_init_alias(ram_above_4g_piecetwo, NULL,
> +                                     "ram-above-4g-piecetwo", ram,
> +                                     0x100000000ULL - holesize, holesize);
> +            memory_region_add_subregion(system_memory,
> +                                        0x100000000ULL +
> +                                        above_4g_mem_size - holesize,
> +                                        ram_above_4g_piecetwo);

Why break it in two?  You can just allocate extra holesize bytes in the
"ram" MemoryRegion, and not map the part that corresponds to
[0x100000000ULL - holesize, 0x100000000ULL).

Also, as Peter said this cannot depend on host considerations.  Just do
it unconditionally, but only for new machine types (pc-1.8 and q35-1.8,
since unfortunately we're too close to hard freeze).

Paolo

> +        } else {
> +            memory_region_init_alias(ram_above_4g, NULL, "ram-above-4g", ram,
> +                                    below_4g_mem_size, above_4g_mem_size);
> +            memory_region_add_subregion(system_memory, 0x100000000ULL,
>                                      ram_above_4g);
> +        }
>      }