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From: Peter Maydell <peter.maydell@linaro.org>
To: Wayne Li <waynli329@gmail.com>
Cc: kvm-devel <kvm@vger.kernel.org>,
	kvm-ppc <kvm-ppc@vger.kernel.org>, qemu-ppc <qemu-ppc@nongnu.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: Problem with virtual to physical memory translation when KVM is enabled.
Date: Tue, 25 Feb 2020 16:16:43 +0000	[thread overview]
Message-ID: <CAFEAcA84xCMzUNfYNBNR8ShA58aor_rbYTq7jnmsLQqhvbOH8w@mail.gmail.com> (raw)
In-Reply-To: <CAM2K0nreUP-zW2pJaH7tWSHHQn7WWeUDoeH_HM99wysgOHANXw@mail.gmail.com>

On Tue, 25 Feb 2020 at 16:10, Wayne Li <waynli329@gmail.com> wrote:
> So what could be causing this problem?  I’m guessing it has something
> to do with the translation lookaside buffers (TLBs)?  But the
> translation between virtual and physical memory clearly works when KVM
> isn’t enabled.  So what could cause this to stop working when KVM is
> enabled?

When you're not using KVM, virtual-to-physical lookups are
done using QEMU's emulation code that emulates the MMU.
When you are using KVM, virtual-to-physical lookups
are done entirely using the host CPU (except for corner
cases like when we come out of the kernel and the user
does things with the gdb debug stub). So all the page
tables and other guest setup of the MMU had better match
what the host CPU expects. (I don't know how big the
differences between e5500 and e6500 MMU are or whether
the PPC architecture/KVM supports emulating the one on
the other: some PPC expert will probably be able to tell you.)

thanks
-- PMM

  reply	other threads:[~2020-02-25 16:16 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-25 16:09 Problem with virtual to physical memory translation when KVM is enabled Wayne Li
2020-02-25 16:16 ` Peter Maydell [this message]
2020-03-03  2:39   ` David Gibson

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