[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Xen PVH support in grub2
On 03/11/17 15:07, Roger Pau Monné wrote: > On Fri, Nov 03, 2017 at 01:50:11PM +0100, Juergen Gross wrote: >> On 03/11/17 13:17, Roger Pau Monné wrote: >>> On Fri, Nov 03, 2017 at 01:00:46PM +0100, Juergen Gross wrote: >>>> On 29/09/17 17:51, Roger Pau Monné wrote: >>>>> On Fri, Sep 29, 2017 at 03:33:58PM +0000, Juergen Gross wrote: >>>>>> On 29/09/17 17:24, Roger Pau Monné wrote: >>>>>>> On Fri, Sep 29, 2017 at 02:46:53PM +0000, Juergen Gross wrote: >>>>>>> Then, I also wonder whether it would make sense for this grub to load >>>>>>> the kernel using the PVH entry point or the native entry point. Would >>>>>>> it be possible to boot a Linux kernel up to the point where cpuid can >>>>>>> be used inside of a PVH container? >>>>>> >>>>>> I don't think today's Linux allows that. This has been discussed >>>>>> very thoroughly at the time Boris added PVH V2 support to the kernel. >>>>> >>>>> OK, I'm not going to insist on that, but my plans for FreeBSD is to >>>>> make the native entry point capable of booting inside of a PVH >>>>> container up to the point where cpuid (or whatever method) can be used >>>>> to detect the environment. >>>> >>>> Looking more thoroughly into the Linux boot code I think this could >>>> work for Linux, too. But only if we can tell PVH from HVM in the guest. >>>> How would you do that in FreeBSD? Via flags in the boot params? This >>>> would the have to be done in the boot loader (e.g. grub or OVMF). >>> >>> My plan was not to differentiate between HVM and PVH, but rather to >>> make use of the ACPI information in order to decide which devices are >>> available and which are not inside of a PVH guest. >>> >>> For example in the FADT "IA-PC Boot Architecture Flags" field for PVH >>> we already set "VGA Not Present" and "CMOS RTC Not Present". There >>> might be other flags/fields that must be set, but I would like to >>> avoid having a CPUID bit or similar saying "PVH", because then Xen >>> will be tied to always providing the same set of devices in PVH >>> containers. >> >> Why? This would depend on the semantics tied to the flag. It could just >> mean "don't assume availability of legacy stuff" (e.g. BIOS calls). >> >> Linux would have a problem with the ACPI approach as it would try BIOS >> calls way before it is initializing its ACPI handling. So in Linux I'd >> need another way to tell I'm running in PVH mode, e.g. a "no legacy" >> bit in the Xen HVM cpuid leaf. > > If you are booted from the PVH entry point, there's no BIOS or UEFI > (ie: no firmware), if you are booted from the BIOS entry point there's > a BIOS and the same applies to UEFI. How does Linux differentiate > whether it's booted from BIOS or UEFI? They use different entries. Juergen _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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