Re: Sharing variables/memory between host and guest ?
Arn wrote: How can one share memory (a few variables not necessarily a page) between host/hypervisor and guest VM ? If you use the -mem-path qemu option, all guest memory will be in a file on tmpfs. You can mmap that file and access all guest memory. Of course, this is hitting the problem with a fairly bit hammer; more refined approaches are possible. Could you outline the other approaches ? Have qemu expose the shared memory as a pci device, and write a guest driver to exploit it. This is what the vga emulation does. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Sharing variables/memory between host and guest ?
How can one share memory (a few variables not necessarily a page) between host/hypervisor and guest VM ? If you use the -mem-path qemu option, all guest memory will be in a file on tmpfs. You can mmap that file and access all guest memory. Of course, this is hitting the problem with a fairly bit hammer; more refined approaches are possible. Could you outline the other approaches ? Thanks arn -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Sharing variables/memory between host and guest ?
Arn wrote: How can one share memory (a few variables not necessarily a page) between host/hypervisor and guest VM ? Since the guest is just a process within the host, there should be existing ways to do this. It's not that straight forward since the host has its pfn (page frame number) while the guest has gfn (guest frame number) and also use virtual memory. What about using something like debugfs or sysfs, is it possible to share variables this way ? Note, I want a system that is fast, i.e. changes to shared variable/memory should be visible instantly. A paravirtualized driver can take care of that with driver in the guest and device side in qemu/host kernel. You can use 9p virtio solution in Linux that implements a shared file system. I search the kvm-devel archives and found emails referring to kshmem but a search on the kvm-70 code turns up nothing. There are also some emails on sharing a page but no final outcome or what exactly to do. Thanks Arn -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Sharing variables/memory between host and guest ?
Thanks Dor. More below. How can one share memory (a few variables not necessarily a page) between host/hypervisor and guest VM ? Since the guest is just a process within the host, there should be existing ways to do this. It's not that straight forward since the host has its pfn (page frame number) while the guest has gfn (guest frame number) and also use virtual memory. So does this mean that there is no way to share a page between host and guest like can be done in Xen ? Wouldn't such a feature be useful ? What about using something like debugfs or sysfs, is it possible to share variables this way ? Note, I want a system that is fast, i.e. changes to shared variable/memory should be visible instantly. A paravirtualized driver can take care of that with driver in the guest and device side in qemu/host kernel. You can use 9p virtio solution in Linux that implements a shared file system. I had a look at the 9p related slides on the KVMForum 2008 page on the wiki and it may serve my purpose but I need to investigate more. According to the slides 9p has been in Linux since 2.6.14 . I'm currently using linux kernel 2.6.22-14 (ubuntu 7.10) with a downloaded kvm-70 . Is this enough for using 9p with KVM or do i need a newer linux kernel ? While on this topic I'd like to point out that its a bit difficult to understand which version of kvm maps to which linux kernel. The page on the wiki is dated. Is it ok to use a kvm-70 module with a slightly older linux kernel ? thanks for you help arn -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Sharing variables/memory between host and guest ?
On Sat, Jul 12, 2008 at 4:03 PM, Arn [EMAIL PROTECTED] wrote: A paravirtualized driver can take care of that with driver in the guest and device side in qemu/host kernel. You can use 9p virtio solution in Linux that implements a shared file system. I had a look at the 9p related slides on the KVMForum 2008 page on the wiki and it may serve my purpose but I need to investigate more. According to the slides 9p has been in Linux since 2.6.14 . I'm currently using linux kernel 2.6.22-14 (ubuntu 7.10) with a downloaded kvm-70 . Is this enough for using 9p with KVM or do i need a newer linux kernel ? The virtio portions of the kernel were just added in 2.6.24, the server portion has not yet been integrated into the kvm-qemu mainline, but is fairly trivial to merge. You can also use the TCP/IP version of the 9p transport to get access to synthetic file systems until all the virtio stuff gets merged. If you really want to stick with the 2.6.22 kernel, it may be possible to build 9p modules with the back ported virtio changes (in fact we were doing just that for a bit). -eric -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Sharing variables/memory between host and guest ?
Eric, thanks for the prompt response, a few more questions: The virtio portions of the kernel were just added in 2.6.24, the server portion has not yet been integrated into the kvm-qemu mainline, but is fairly trivial to merge. You can also use the TCP/IP version of the 9p transport to get access to synthetic file systems until all the virtio stuff gets merged. What exactly is kvm-qemu mainline ? Is it the qemu parts of KVM that have been merged into the kernel ? Could you point to which directory of the kernel code this refers to (also kernel version) ? Also would this be a fast way to share a few variables between guest and host ? If you really want to stick with the 2.6.22 kernel, it may be possible to build 9p modules with the back ported virtio changes (in fact we were doing just that for a bit). No, I can upgrade my kernel. I just need to know which one I should use. Should I just go with the latest stable 2.6.25.10 kernel with kvm-70 module ? Thanks arn -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Sharing variables/memory between host and guest ?
On Sat, Jul 12, 2008 at 4:59 PM, Arn [EMAIL PROTECTED] wrote: Eric, thanks for the prompt response, a few more questions: The virtio portions of the kernel were just added in 2.6.24, the server portion has not yet been integrated into the kvm-qemu mainline, but is fairly trivial to merge. You can also use the TCP/IP version of the 9p transport to get access to synthetic file systems until all the virtio stuff gets merged. What exactly is kvm-qemu mainline ? Is it the qemu parts of KVM that have been merged into the kernel ? Could you point to which directory of the kernel code this refers to (also kernel version) ? I'm talking about the kvm-userspace pieces, not kernel pieces. -eric -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Sharing variables/memory between host and guest ?
How can one share memory (a few variables not necessarily a page) between host/hypervisor and guest VM ? Since the guest is just a process within the host, there should be existing ways to do this. What about using something like debugfs or sysfs, is it possible to share variables this way ? Note, I want a system that is fast, i.e. changes to shared variable/memory should be visible instantly. I search the kvm-devel archives and found emails referring to kshmem but a search on the kvm-70 code turns up nothing. There are also some emails on sharing a page but no final outcome or what exactly to do. Thanks Arn -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
