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Date: Sun, 22 Oct 2006 17:23:48 +0200 From: Arnd Bergmann <arnd@...db.de> To: Avi Kivity <avi@...ranet.com> Cc: Muli Ben-Yehuda <muli@...ibm.com>, linux-kernel <linux-kernel@...r.kernel.org>, Anthony Liguori <aliguori@...ibm.com>, Alan Cox <alan@...rguk.ukuu.org.uk> Subject: Re: [PATCH 0/7] KVM: Kernel-based Virtual Machine On Sunday 22 October 2006 10:37, Avi Kivity wrote: > I like this. Since we plan to support multiple vcpus per vm, the fs > structure might look like: > > /kvm/my_vm > | > +----memory # mkdir to create memory slot. Note that the way spufs does it, every directory is a reference-counted object. Currently that includes single contexts and groups of contexts that are supposed to be scheduled simultaneously. The trick is that we use the special 'spu_create' syscall to add a new object, while naming it, and return an open file descriptor to it. When that file descriptor gets closed, the object gets garbage-collected automatically. This way you can simply kill a task, which also cleans up all the special objects it allocated. We ended up adding a lot more file than we initially planned, but the interface is really handy, especially if you want to create some procps-like tools for it. > | | # how to set size and offset? > | | > | +---0 # guest physical memory slot > | | > | +-- dirty_bitmap # read to get and atomically reset > | # the changed pages log Have you thought about simply defining your guest to be a section of the processes virtual address space? That way you could use an anonymous mapping in the host as your guest address space, or even use a file backed mapping in order to make the state persistant over multiple runs. Or you could map the guest kernel into the guest real address space with a private mapping and share the text segment over multiple guests to save L2 and RAM. > | > | > +----cpu # mkdir/rmdir to create/remove vcpu > | I'd recommend not allowing mkdir or similar operations, although it's not that far off. One option would be to let the user specify the number of CPUs at kvm_create() time, another option might be to allow kvm_create with a special flag or yet another syscall to create the vcpu objects. > +----0 > | | > | +--- irq # write to inject an irq > | | > | +--- regs # read/write to get/set registers > | | > | +--- debugger # write to set breakpoints/singlestep mode > | > +----1 > [...] > > It's certainly a lot more code though, and requires new syscalls. Since > this is a little esoteric does it warrant new syscalls? We've gone through a number of iterations on the spufs design regarding this, and in the end decided that the garbage-collecting property of spu_create was superior to any other option, and adding the spu_run syscall was then the logical step. BTW, one inspiration for spu_run came from sys_vm86, which as you are probably aware of is already doing a lot of what you do, just not for protected mode guests. Arnd <>< - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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