Re: [kvm-devel] portability layer?
Hollis Blanchard wrote: >> No, I'm saying that some #ifdeffery in both libkvm and the ioctl >> interface is unavoidable. >> > > If by #ifdeffery you mean having per-architecture definitions of > structures like kvm_regs, absolutely. If you mean literal #ifdefs in the > middle a header file, I believe that can and should be avoided. > > If it can be avoided I'm all for it. >> Right now this is handled by qemu, which means our higher level tools >> are _already_ nonportable. >> > > Yes, but not *all* the higher level tools are. At some point you have a > common interface, and at this point I think I've answered my own > question: the qemu monitor connection is the portable interface. > > That means everything layered above qemu, such as libvirt and thus > virt-manager, should work on all architectures +/- without changes. > Lower-level software, such as GDB, would need per-architecture support. > > Ah, _those_ higher layer tools. Each of these interfaces needs to be stabilized for different reasons: - the kernel ABI allows the kernel and userspace to be upgraded independently - libkvm is mainly for when we've merged all our changes into mainline qemu, and for the theoretical second user - the qemu monitor is for the higher level tools Note that the qemu monitor (and commandline) interface is under the control of the qemu maintainers, not us. So far it has been steadily improving. >> [I have a feeling we're talking a little past each other, probably due >> to me not knowing ppc at any level of detail. No doubt things will >> become clearer when the code arrives] >> > > I don't have any code for you, but you will be the first to know when I > do. :) Right now I'm just trying to make sure we don't accidentally > paint ourselves into a corner with a stable ABI. > The stable ABI here is just the support baseline, not a freeze. We know for certain that changes are needed for smp, paravirt drivers, new hardware virtualization extensions, and new archs. And of course it only holds for x86; other archs will stabilize when they are ready. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. - Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV ___ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
Re: [kvm-devel] portability layer?
On Wed, 2007-03-28 at 17:48 +0200, Avi Kivity wrote: > Hollis Blanchard wrote: > > On Tue, 2007-03-27 at 08:57 +0200, Avi Kivity wrote: > >> > >> I don't think we should be aiming at full source portability. > >> Virtualization is inherently nonportable, and as it is mostly done in > >> hardware, software gets to do the quirky stuff that the hardware people > >> couldn't bother with :) instead we should be aiming at code reuse. > >> > > > > I'm not sure I see the distinction you're making. Operating systems > > could also be considered "inherently nonportable", yet Linux and the > > BSDs support an enormous range of platforms. If you're saying that we > > shouldn't try to run x86 MMU code on a PowerPC then I can't agree > > more. :) > > No, I'm saying that some #ifdeffery in both libkvm and the ioctl > interface is unavoidable. If by #ifdeffery you mean having per-architecture definitions of structures like kvm_regs, absolutely. If you mean literal #ifdefs in the middle a header file, I believe that can and should be avoided. > Right now this is handled by qemu, which means our higher level tools > are _already_ nonportable. Yes, but not *all* the higher level tools are. At some point you have a common interface, and at this point I think I've answered my own question: the qemu monitor connection is the portable interface. That means everything layered above qemu, such as libvirt and thus virt-manager, should work on all architectures +/- without changes. Lower-level software, such as GDB, would need per-architecture support. > [I have a feeling we're talking a little past each other, probably due > to me not knowing ppc at any level of detail. No doubt things will > become clearer when the code arrives] I don't have any code for you, but you will be the first to know when I do. :) Right now I'm just trying to make sure we don't accidentally paint ourselves into a corner with a stable ABI. -Hollis - Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV ___ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
Re: [kvm-devel] portability layer?
Hollis Blanchard wrote: > On Tue, 2007-03-27 at 08:57 +0200, Avi Kivity wrote: > >> Hollis Blanchard wrote: >> >>> Hi Avi, I was wondering what you think is the right abstraction layer to >>> target for porting KVM to non-x86 architectures? To me it looks like >>> libkvm is the answer. >>> >>> The kernel/userland interface is heavily x86-specific, including things >>> like struct kvm_run. So it looks like the higher-level API of >>> kvm_init(), kvm_create(), etc would be the right cut? struct >>> kvm_callbacks is even reasonably portable, especially if cpuid is hidden >>> behind an "arch" callback. >>> >>> >> Disclaimer: I know little about powerpc (or ia64). What I say may or >> may not have any connection with reality. >> >> I don't think we should be aiming at full source portability. >> Virtualization is inherently nonportable, and as it is mostly done in >> hardware, software gets to do the quirky stuff that the hardware people >> couldn't bother with :) instead we should be aiming at code reuse. >> > > I'm not sure I see the distinction you're making. Operating systems > could also be considered "inherently nonportable", yet Linux and the > BSDs support an enormous range of platforms. If you're saying that we > shouldn't try to run x86 MMU code on a PowerPC then I can't agree > more. :) > No, I'm saying that some #ifdeffery in both libkvm and the ioctl interface is unavoidable. A trivial example is kvm_get_regs(). If you want to do anything other than memcpy() the result, the caller has to be nonportable. kvm_setup_cpuid() doesn't make sense on ppc, as you said. The in*/out* callbacks don't belong, and there will probably be a few callbacks that will leave me puzzled when you add them. The fact is that the "higher level tools" will emulate a powerpc when running on a powerpc, and an x86 when running on an x86. That's different from a webserver which is implementing the http protocol no matter what the underlying platform is. That's what I meant by "inherently nonportable". > Aside from code reuse though (on which I absolutely agree), it's > critical that the interface be the same, i.e. each architecture > implements the same interface in different ways. With that, all the > higher-level tools will work with minimal modification. (This is > analogous to an OS interface like POSIX.) > > A function like sys_read() can be made reasonably portable, but injecting an interrupt into an x86 requires peeking into a register which is aliased to an mmio location (cr8/tpr). No doubt ppc has its own wierdnesses, but they'll be different. Right now this is handled by qemu, which means our higher level tools are _already_ nonportable. >> I think there's some potential there: >> >> - memory slot management, including the dirty log, could be mostly >> reused (possibly updated for multiple page sizes). possibly msrs as well. >> > > I'm not familiar with KVM's memory slots or dirty log. My first > impression was that the dirty log is tied to the x86 shadow pagetable > implementation, but I admit I haven't investigated further. > The implementation is, but the interface and use is generic. The dirty log is used for two purposes: - minimization of screen updates on framebuffer changes - tracking pages which need to be re-copied during live migration Hopefully the interface and some parts of the kernel code can be reused. The memory slots thing is just a way for userspace to specify physically discontiguous memory. Each slot is contiguous within itself, but different slots may be discontiguous. It is used for the framebuffer, and for various memory holes in x86 (640KB-1MB and the pci hole). > >> I don't see a big difference between the ioctl layer and libkvm. In >> general, a libkvm function is an ioctl, and kvm_callback members are a >> decoding of kvm_run fields. If you edit kvm_run to suit your needs, you >> can probably reuse some of it. >> > > kvm_run as it stands is 100% x86-specific. (I doubt it could even be > easily adapted for ia64, which is more similar to x86 than PowerPC.) So > right now the kernel ioctl interface has an architecture-specific > component, which violates the principle of identical interfaces I > described earlier. > Just #ifdef the x86 specific parts away, and add your own magic where necessary. > That means we either a) need to change the kernel interface or b) define > a higher-level interface that *is* identical. That higher-level > interface would be libkvm, hence my original question. > > Does my original question make more sense now? If you make libkvm the > official interface, you would at least need to hide the "cpuid" > callback, since it is intimately tied to an x86 instruction. > Well, libkvm is _an_ official interface. Any changes needed to make it portable are welcome. [I have a feeling we're talking a little past each other, probably due to me not knowing ppc at any level o
Re: [kvm-devel] portability layer?
On Wednesday 28 March 2007, Hollis Blanchard wrote: > > I don't see a big difference between the ioctl layer and libkvm. In > > general, a libkvm function is an ioctl, and kvm_callback members are a > > decoding of kvm_run fields. If you edit kvm_run to suit your needs, you > > can probably reuse some of it. > > kvm_run as it stands is 100% x86-specific. (I doubt it could even be > easily adapted for ia64, which is more similar to x86 than PowerPC.) So > right now the kernel ioctl interface has an architecture-specific > component, which violates the principle of identical interfaces I > described earlier. Remember that there _is_ an equivalent of kvm_run on powerpc (not powerpc64) inside of MacOnLinux, though I could not find it now when looking through the source. > That means we either a) need to change the kernel interface or b) define > a higher-level interface that *is* identical. That higher-level > interface would be libkvm, hence my original question. > > Does my original question make more sense now? If you make libkvm the > official interface, you would at least need to hide the "cpuid" > callback, since it is intimately tied to an x86 instruction. If there is going to be an architecture independent interface, it should really be able to cover s390 as well, which has yet other requirements. It's probably closer to amd64 than to powerpc64 though. Arnd <>< - Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV ___ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
Re: [kvm-devel] portability layer?
On Tue, 2007-03-27 at 08:57 +0200, Avi Kivity wrote: > Hollis Blanchard wrote: > > Hi Avi, I was wondering what you think is the right abstraction layer to > > target for porting KVM to non-x86 architectures? To me it looks like > > libkvm is the answer. > > > > The kernel/userland interface is heavily x86-specific, including things > > like struct kvm_run. So it looks like the higher-level API of > > kvm_init(), kvm_create(), etc would be the right cut? struct > > kvm_callbacks is even reasonably portable, especially if cpuid is hidden > > behind an "arch" callback. > > > > Disclaimer: I know little about powerpc (or ia64). What I say may or > may not have any connection with reality. > > I don't think we should be aiming at full source portability. > Virtualization is inherently nonportable, and as it is mostly done in > hardware, software gets to do the quirky stuff that the hardware people > couldn't bother with :) instead we should be aiming at code reuse. I'm not sure I see the distinction you're making. Operating systems could also be considered "inherently nonportable", yet Linux and the BSDs support an enormous range of platforms. If you're saying that we shouldn't try to run x86 MMU code on a PowerPC then I can't agree more. :) Aside from code reuse though (on which I absolutely agree), it's critical that the interface be the same, i.e. each architecture implements the same interface in different ways. With that, all the higher-level tools will work with minimal modification. (This is analogous to an OS interface like POSIX.) > I think there's some potential there: > > - memory slot management, including the dirty log, could be mostly > reused (possibly updated for multiple page sizes). possibly msrs as well. I'm not familiar with KVM's memory slots or dirty log. My first impression was that the dirty log is tied to the x86 shadow pagetable implementation, but I admit I haven't investigated further. > - the vcpu management calls (get regs/set regs, vcpu_run) can be > reused, but only as wrappers. The actual contents (including the > kvm_run structure) would be very different. Right, each architecture would define its own, and all code that touches these data structures would be moved out of common code. > I don't see a big difference between the ioctl layer and libkvm. In > general, a libkvm function is an ioctl, and kvm_callback members are a > decoding of kvm_run fields. If you edit kvm_run to suit your needs, you > can probably reuse some of it. kvm_run as it stands is 100% x86-specific. (I doubt it could even be easily adapted for ia64, which is more similar to x86 than PowerPC.) So right now the kernel ioctl interface has an architecture-specific component, which violates the principle of identical interfaces I described earlier. That means we either a) need to change the kernel interface or b) define a higher-level interface that *is* identical. That higher-level interface would be libkvm, hence my original question. Does my original question make more sense now? If you make libkvm the official interface, you would at least need to hide the "cpuid" callback, since it is intimately tied to an x86 instruction. -Hollis - Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV ___ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
Re: [kvm-devel] portability layer?
Hollis Blanchard wrote: > Hi Avi, I was wondering what you think is the right abstraction layer to > target for porting KVM to non-x86 architectures? To me it looks like > libkvm is the answer. > > The kernel/userland interface is heavily x86-specific, including things > like struct kvm_run. So it looks like the higher-level API of > kvm_init(), kvm_create(), etc would be the right cut? struct > kvm_callbacks is even reasonably portable, especially if cpuid is hidden > behind an "arch" callback. > Disclaimer: I know little about powerpc (or ia64). What I say may or may not have any connection with reality. I don't think we should be aiming at full source portability. Virtualization is inherently nonportable, and as it is mostly done in hardware, software gets to do the quirky stuff that the hardware people couldn't bother with :) instead we should be aiming at code reuse. I think there's some potential there: - memory slot management, including the dirty log, could be mostly reused (possibly updated for multiple page sizes). possibly msrs as well. - the vcpu management calls (get regs/set regs, vcpu_run) can be reused, but only as wrappers. The actual contents (including the kvm_run structure) would be very different. I don't see a big difference between the ioctl layer and libkvm. In general, a libkvm function is an ioctl, and kvm_callback members are a decoding of kvm_run fields. If you edit kvm_run to suit your needs, you can probably reuse some of it. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. - Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV ___ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
