Re: [Minios-devel] [PATCH 30/40] arm64: set the mapping for console and xenbus

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 08/11/17 09:11, Huang Shijie wrote:
> On Mon, Nov 06, 2017 at 05:31:43PM +0000, Julien Grall wrote:
> > Hi Shijie,
> >
> > On 03/11/17 03:12, Huang Shijie wrote:
> > > This patch sets the mapping for console and xenbus:
> > >      .1) Use the page granule (4K) to setup the page table.
> > This should belong to the patch building page-table.
> Please just keep it here..
>
> This is the first place where we use the 4k page size.
See my answer in that patch...

[...]

> > As you can't assume where it the console/xenbus frame in the memory layout,
> > there are chance the virtual addresses will be well above 39-bits. Resulting
> > to an access fault.
> 39bit is 512G. Does the mini-os can beyond 512G memory? >
> There is no virtual address above 39-bits now. If it really exits, we
> can extand the address space to 64-bits.
You should really look at how you implemented to_virt and think how the 
conversion will happen depending on the physical address...
> > So you should allocate the virtual address on demand. You can look what x86
> > does.
> I will check that.
> > This will also benefits when we will need to map lists of MFN in a
> > contiguous way in the VA space.
> >
> > > +
> > > +    build_pagetable(vaddr, mfn, 1, BLOCK_DEF_ATTR, alloc_new_page, 3);
> > I am a bit surprised that build_pagetable does not return an error. At least
> > it may not be possible to allocate page-table.
> If the build_pagetable() fails, it will reach the BUG().
>
> If we need the return value of build_pagetable(), we can add it in
> future. But currently, it is okay.
Do it need now. Full stop. There are no rationale reason to not write 
the page-table correctly from scratch... And no, you don't save time at 
all by deferring it.
Cheers,

--
Julien Grall

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