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

[Aurelien Jarno]

On Fri, Jun 20, 2014 at 02:07:05AM -0400, Paolo Bonzini wrote:
> 
> 
> ----- Messaggio originale -----
> > Da: "Aurelien Jarno" <address@hidden>
> > A: "Sanjay Lal" <address@hidden>
> > Cc: "James Hogan" <address@hidden>, address@hidden, "Peter Maydell" 
> > <address@hidden>,
> > address@hidden, "Gleb Natapov" <address@hidden>, "Paolo Bonzini" 
> > <address@hidden>
> > 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 <address@hidden> 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?

For what I understand the current KVM support in MIPS uses trap and
emulate and thus doesn't need hardware support, just a recent kernel
with the option enabled. That's why I do wonder if there is a real point
in supporting UM kernels in TCG mode.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
address@hidden                 http://www.aurel32.net