Re: [PATCH 1/2] kvm tools: Add memory gap for larger RAM sizes

[Avi Kivity <avi@redhat.com>]

On 05/11/2011 08:37 AM, Pekka Enberg wrote:
> On Wed, May 11, 2011 at 12:05 AM, Sasha Levin<levinsasha928@gmail.com>  wrote:
> >  +       if (kvm->ram_size<  0xe0000000) {
>
> Please use the ULL postfix for constants to ensure the types are sane.
> Also, please come up with a sane name for these.
>
> >  @@ -60,7 +60,14 @@ static inline u32 segment_to_flat(u16 selector, u16 offset)
> >
> >    static inline void *guest_flat_to_host(struct kvm *self, unsigned long offset)
> >    {
> >  -       return self->ram_start + offset;
> >  +       /*
> >  +        * We have a gap between 0xe0000000 and 0x100000000.
> >  +        * Consider it when translating an address above 0x100000000.
> >  +        */
> >  +       if (offset<  0xe0000000)
> >  +               return self->ram_start + offset;
> >  +       else
> >  +               return self->ram_start + 0xe0000000 + (offset - 0x100000000);
> >    }
>
> Would it not be simpler to mmap() a "ram_size + gap_size" contiguous
> region and mprotect(PROT_NONE) the gap? We'd still tell KVM and E820
> maps about two separate regions but guest_flat_to_host() would
> work-as-is.

It doesn't work in general - if you have a PCI device with a BAR (like a 
video card framebuffer), then you need allocations for main memory (0+) 
and pci (0xe000000+).  You can't have a contiguous mapping on i386 
containing both.

-- 
error compiling committee.c: too many arguments to function