Hi, On 20/06/14 07:07, Paolo Bonzini wrote: > ----- Messaggio originale ----- >> Da: "Aurelien Jarno" <aurel...@aurel32.net> >> A: "Sanjay Lal" <sanj...@kymasys.com> >> Cc: "James Hogan" <james.ho...@imgtec.com>, qemu-de...@nongnu.org, "Peter >> Maydell" <peter.mayd...@linaro.org>, >> kvm@vger.kernel.org, "Gleb Natapov" <g...@redhat.com>, "Paolo Bonzini" >> <pbonz...@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 <aurel...@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.
I did recently try relocating the bootloader to the reset address in the T&E KSeg0 (i.e. PA=0x1fc00000, VA=0x5fc00000), but the current MIPS KVM implementation in the kernel has some limitations when it comes to memory regions. It allocates a linear guest_pmap array (for GPA->RPA page mapping) based only on the first memory region committed, so if you set e.g. mem=64MB then physical memory according to guest_pmap won't reach the reset address and it fails to map it. The kernel needs fixing to use a more flexible physical page table structure first really. >> 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, FYI I tried this and it was a fairly small change (fixing CP0_EBase initialisation and switching a couple of kvm_enabled() checks to something like mips_um_ksegs_enabled()). Needs more testing though. > while umkernel=off with KVM requires virtualization extensions. > > The same option can disable pflash boot. > > What do you think? I think with an executable flash region / reset address the pflash option could be made to work, but of course you'd probably need a relocated flash image too, which may make the option less useful (and it presumably isn't like a kernel ELF where you can detect what address it's linked). For now disabling Malta non kernel loads in KVM mode makes sense I think. Thanks James -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
