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
