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Re: [PATCH 0/8] Simplify memory_region_add_subregion_overlap(..., priori
From: |
Peter Maydell |
Subject: |
Re: [PATCH 0/8] Simplify memory_region_add_subregion_overlap(..., priority=0) |
Date: |
Mon, 16 Dec 2019 11:46:35 +0000 |
On Mon, 16 Dec 2019 at 11:40, Michael S. Tsirkin <address@hidden> wrote:
>
> On Sun, Dec 15, 2019 at 03:27:12PM +0000, Peter Maydell wrote:
> > On Sun, 15 Dec 2019 at 09:51, Michael S. Tsirkin <address@hidden> wrote:
> > >
> > > On Sat, Dec 14, 2019 at 04:28:08PM +0000, Peter Maydell wrote:
> > > > (It doesn't actually assert that it doesn't
> > > > overlap because we have some legacy uses, notably
> > > > in the x86 PC machines, which do overlap without using
> > > > the right function, which we've never tried to tidy up.)
> > >
> > > It's not exactly legacy uses.
> > >
> > > To be more exact, the way the non overlap versions
> > > are *used* is to mean "I don't care what happens when they overlap"
> > > as opposed to "will never overlap".
> >
> > Almost all of the use of the non-overlap versions is
> > for "these are never going to overlap" -- devices or ram at
> > fixed addresses in the address space that can't
> > ever be mapped over by anything else. If you want
> > "can overlap but I don't care which one wins" then
> > that would be more clearly expressed by using the _overlap()
> > version but just giving everything that can overlap there
> > the same priority.
>
> Problem is device doesn't always know whether something can overlap it.
> Imagine device A at a fixed address.
> Guest can program device B to overlap the fixed address.
> How is device A supposed to know this can happen?
That's why (the original intention was) only one of the
regions needs to be marked 'overlap OK', not both.
thanks
-- PMM
- [PATCH 5/8] hw/mips/boston: Use memory_region_add_subregion() when priority is 0, (continued)
- [PATCH 5/8] hw/mips/boston: Use memory_region_add_subregion() when priority is 0, Philippe Mathieu-Daudé, 2019/12/14
- [PATCH 7/8] target/i386: Use memory_region_add_subregion() when priority is 0, Philippe Mathieu-Daudé, 2019/12/14
- [PATCH 4/8] hw/i386/intel_iommu: Use memory_region_add_subregion when priority is 0, Philippe Mathieu-Daudé, 2019/12/14
- Re: [PATCH 0/8] Simplify memory_region_add_subregion_overlap(..., priority=0), Peter Maydell, 2019/12/14
- Re: [PATCH 0/8] Simplify memory_region_add_subregion_overlap(..., priority=0), Michael S. Tsirkin, 2019/12/15