Messages in this thread | | | Subject | Re: [PATCH 2/2] xen/pv: Call get_cpu_address_sizes to set x86_virt/phys_bits | From | "M. Vefa Bicakci" <> | Date | Sun, 22 Jul 2018 11:57:39 -0400 |
| |
On 07/21/2018 07:17 PM, M. Vefa Bicakci wrote: > On 07/21/2018 05:25 PM, Boris Ostrovsky wrote: >> On 07/21/2018 03:49 PM, M. Vefa Bicakci wrote: >>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c >>> index 439a94bf89ad..87afb000142a 100644 >>> --- a/arch/x86/xen/enlighten_pv.c >>> +++ b/arch/x86/xen/enlighten_pv.c >>> @@ -1257,6 +1257,7 @@ asmlinkage __visible void __init xen_start_kernel(void) >>> /* Work out if we support NX */ >>> get_cpu_cap(&boot_cpu_data); >>> + get_cpu_address_sizes(&boot_cpu_data); >>> x86_configure_nx(); >> >> >> Have you observed any problems without this call? get_cpu_cap() is only >> called here to set X86_FEATURE_NX, and is then called again, together >> with get_cpu_address_sizes(), from early_identify_cpu(). > > Thank you for the reviews! Without the call to get_cpu_address_sizes, > paravirtualized virtual machines do not boot up kernels with versions > 4.17 and up at all; this includes dom0 and domU. No domU logs are > generated in dom0's /var/log/xen/console/ directory either, despite > having earlyprintk=xen on the kernel command line for my test domU.
Hello Boris,
I debugged this further with a debugging version of Xen (so that I can get early kernel print-outs via the "xen_raw_console_write" function), and I found the root cause of the boot up failure.
In summary, the issue is due to the following call path in version 4.17 (and higher, I assume), which the kernel goes through /only/ when CONFIG_DEBUG_VIRTUAL is enabled:
enlighten_pv.c::xen_start_kernel mmu_pv.c::xen_reserve_special_pages page.h::__pa physaddr.c::__phys_addr physaddr.h::phys_addr_valid // uses boot_cpu_data.x86_phys_bits
The return value of phys_addr_valid is used with the VIRTUAL_BUG_ON macro, which evaluates to BUG_ON in case CONFIG_DEBUG_VIRTUAL is enabled.
It looks like the call to get_cpu_address_size is required in the xen_start_kernel function. Perhaps there is a more elegant way to resolve this issue as well.
Another approach could be to check in the phys_addr_valid function whether boot_cpu_data.x86_phys_bits has been initialized or not, I think, but I am not sure about the correctness of this approach.
Thank you,
Vefa
| |