[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] Default for phys-addr-bits? (was Re: [PATCH 4/5] x86: A

From: Paolo Bonzini
Subject: Re: [Qemu-devel] Default for phys-addr-bits? (was Re: [PATCH 4/5] x86: Allow physical address bits to be set)
Date: Wed, 22 Jun 2016 16:33:18 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1

On 22/06/2016 16:24, Andrea Arcangeli wrote:
> Linux could not possibly crash instead if host phys bits > guest phys
> bits because it will never depend on GPF triggering if the must be
> zero bits of the guest pagetables are set. Linux won't ever try to set
> those bits and I'd be shocked if any other OS does.

Well, KVM does.  It sets _all_ bits up to 51, not just one, but still we
have a counterexample.

The reason to do this is that you can distinguish a not-present from a
present-reserved page fault, and handle the present-reserved page fault
from a cache without having to walk the page tables.


> So while not perfect emulation of the hardware, the risk with known OS
> should be zero.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]