[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] Re: [Xen-changelog] Indirect hypercalls through ahypercall transfer page.
> > The hypercall transfer page is just one of several new > feature flags > > that should enable us to have a single xen-ified kernel that is > > capable of running on bare metal, on pae and non-pae > hypervisors, 64b > > A 32-bit kernel running on a 64-bit xen, for example? So in > this case xen fills the page with 32-bit hcalls? Our current priority developing xen feature flags has been to enable xenified kernels to run on bare metal and to allow non-PAE kernels on a PAE hypervisor, but 32 on 64 is certainly something it would be good to support too. The key feature flag we're still missing is the ability for the guest kernel to query the size of the 'hypervisor hole' at boot time, and then adjust its VM layout appropriately. Conceptually, this is quite simple for Linux -- just turn HYPERVISOR_VIRTSTART into a variable. Unfortunately, things are a little more complicated: right at the top of the kernel's virtual address space is the fixaddr region. The vsyscall page lives within the fixaddr region, and its virtual address needs to be known at *compile* time as it gets built into various elf objects. A number of options are aviable to fix this 1) provide either kernel or domain builder support for relocating the syscall page (sounds hard); 2) move the vsyscall page out of fixmap and put it somewhere toward the bottom of the virtual address space; 3) move the vsyscall page out of fixmap and put it just below the kernel address space (i.e. top of user space). The latter is the currently favoured option, as recommended by Andi (it's also used by the x86_64 ia32 compat layer). I'm hoping we can get this in before the SLES10 xen kernel gets finalized. Ian _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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