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

[Li Zhijian]

On 11/30/2018 10:53 PM, Michael S. Tsirkin wrote:
> 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

okay, thanks


> > initrd_max to 4G - 1 simply is enough if
> > this bit is set.
> >
> > CC: Paolo Bonzini <address@hidden>
> > CC: Richard Henderson <address@hidden>
> > CC: Eduardo Habkost <address@hidden>
> > CC: "Michael S. Tsirkin" <address@hidden>
> > CC: Marcel Apfelbaum <address@hidden>
> > Signed-off-by: Li Zhijian <address@hidden>
> > ---
> >   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?

Okay, i will import this header at V3


> >   
> >   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

Okay


> > +        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 ...

Got it, thanks again


Thanks
Zhijian


> > 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
>
> .