Re: [Xen-devel] Re: [PATCH] Add a new p2m type for broken memory

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 14/07/2010 14:41, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

>> You should probably do this in more places, even if you don't care
>> about shadow pagetables -- MMIO emulation should behave the same as
>> normal accesses.
> 
> What do you mean of " the same as normal access"?
> MMIO will not be poisoned and will not be marked as p2m_ram_broken. We only
> need track guest's access to poison RAM.
> 
> There are some case need considered, like hypervisor emulate instruction for
> guest. For example, considering "movs (*rsi), (*rdi)", where rdi points to
> MMIO or APIC, while rsi points to poison memory. However, In such situation,
> it will trigger EPT fault firstly and cause the guest be crashed (I tested
> movs from poison memory to apic range). As there is no prefetch in EPT
> situation if I understand correctly, I assume it should be ok at least for EPT
> guest.

I doubt it's architecturally guaranteed. What about edge cases like 'PUSH
mem' from an MMIO location, destination is stack, pointer to which has just
crossed a page boundary to a broken page? I don't think it's hard to fill in
the blanks for emulation of guest instructions so you might as well do so.

 -- Keir



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