Re: [Qemu-devel] [PATCH v2 5/5] x86: allow load initrd below 4G for recent linux

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 21, 2018 at 10:06:06AM +0800, Li Zhijian wrote:
> a new field xloadflags was added to recent x86 linux, and BIT 1:
> XLF_CAN_BE_LOADED_ABOVE_4G is used to tell bootload that where initrd can be
> loaded saftly.

safely

> 
> Current QEMU always load

loads

> initrd below below_4g_mem_size which

is

> always
> less than 4G, so here limit


limiting

> initrd_max to 4G - 1 simply is enough if
> this bit is set.
> 
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Richard Henderson <rth@twiddle.net>
> CC: Eduardo Habkost <ehabkost@redhat.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> ---
>  hw/i386/pc.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 2ffe6fb..6d4b973 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -92,6 +92,7 @@
>  #define FW_CFG_HPET (FW_CFG_ARCH_LOCAL + 4)
>  
>  #define E820_NR_ENTRIES		16
> +#define XLF_CAN_BE_LOADED_ABOVE_4G_MASK (1 << 1)

why not XLF_CAN_BE_LOADED_ABOVE_4G to be consistent
with Linux?
In fact let's import include/uapi/asm/bootparam.h
into standard-headers, and use the macro from there?


>  
>  struct e820_entry {
>      uint64_t address;
> @@ -916,6 +917,17 @@ static void load_linux(PCMachineState *pcms,
>      } else {
>          initrd_max = 0x37ffffff;
>      }
> +    if (protocol >= 0x20c) {

Let's move it above so we have

if (protocol >= 20c)
else if 0x203
else


> +        unsigned int xloadflags = lduw_p(header+0x236);
> +        if (xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G_MASK) {
> +                /*
> +                 * Although kernel allow

allows

> initrd loading to above 4G, here we
> +                 * limit initrd_max to 4G -1


Well not really, it just makes it as large as possible
while still staying below 4G.

> due to

since

> current QEMU always loads
> +                 * initrd

It's not QEMU, is it? It's actually the bios ...

> below pcms->below_4g_mem_size
> +                 */
> +                initrd_max = UINT32_MAX;
> +        }
> +    }
>  
>      if (initrd_max >= pcms->below_4g_mem_size - pcmc->acpi_data_size) {
>          initrd_max = pcms->below_4g_mem_size - pcmc->acpi_data_size - 1;
> -- 
> 2.7.4