Re: [PATCH v5 10/12] hw/mips: malta: Add KVM support

[Paolo Bonzini <pbonzini@redhat.com>]

----- Messaggio originale -----
> Da: "Aurelien Jarno" <aurelien@aurel32.net>
> A: "Sanjay Lal" <sanjayl@kymasys.com>
> Cc: "James Hogan" <james.hogan@imgtec.com>, qemu-devel@nongnu.org, "Peter Maydell" <peter.maydell@linaro.org>,
> kvm@vger.kernel.org, "Gleb Natapov" <gleb@redhat.com>, "Paolo Bonzini" <pbonzini@redhat.com>
> Inviato: Giovedì, 19 giugno 2014 23:47:34
> Oggetto: Re: [Qemu-devel] [PATCH v5 10/12] hw/mips: malta: Add KVM support
> 
> On Thu, Jun 19, 2014 at 12:34:24PM -0700, Sanjay Lal wrote:
> > 
> > On Jun 19, 2014, at 9:27 AM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> > 
> > > On Tue, Jun 17, 2014 at 11:10:35PM +0100, James Hogan wrote:
> > >> In KVM mode the bootrom is loaded and executed from the last 1MB of
> > >> DRAM.
> > > 
> > > What is the reason for that? I am not opposed to that, but if it is
> > > really needed, it means that loading a bootloader into the flash area
> > > (for example YAMON) won't work and that this should be forbidden to the
> > > user.
> > > 
> > 
> > In trap and emulate mode, both the kernel and userland run in user mode on
> > the processor. Virtual addresses >= 0x80000000 are only accessible in
> > kernel mode, and the default flash area (VA: 0xbfc00000/PA: 0x1fc00000)
> > falls in this range.
> > 
> > We therefore decided to relocate the bootloader to the last 1MB of RAM.
> > This area is excluded from the RAM ranges supplied to the kernel, so it
> > should not be accessible to the user.
> > 
> 
> Thanks for the explanation. It means we should disable the support for
> booting from the flash (using -pflash) in KVM mode, as it would simply
> not work.

My idea was to add a machines-specific option umkernel=on, and require it
in order to run KVM.  Later we can add umkernel=on support for TCG as well,
while umkernel=off with KVM requires virtualization extensions.

The same option can disable pflash boot.

What do you think?

Paolo