From: "M. Vefa Bicakci" <m.v.b@runbox.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
linux-kernel@vger.kernel.org
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Juergen Gross <jgross@suse.com>,
xen-devel@lists.xenproject.org, x86@kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH 2/2] xen/pv: Call get_cpu_address_sizes to set x86_virt/phys_bits
Date: Sun, 22 Jul 2018 11:57:39 -0400 [thread overview]
Message-ID: <13b774d7-bc8c-039a-fbc0-52318f535883@runbox.com> (raw)
In-Reply-To: <d85c93da-4549-a7c1-af48-9c62cba8ae71@runbox.com>
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
next prev parent reply other threads:[~2018-07-22 15:58 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-21 19:49 [PATCH 1/2] x86/entry/64: Do not clear %rbx under Xen M. Vefa Bicakci
2018-07-21 19:49 ` [PATCH 2/2] xen/pv: Call get_cpu_address_sizes to set x86_virt/phys_bits M. Vefa Bicakci
2018-07-21 21:25 ` Boris Ostrovsky
2018-07-21 23:17 ` M. Vefa Bicakci
2018-07-22 15:57 ` M. Vefa Bicakci [this message]
2018-07-23 15:04 ` Boris Ostrovsky
2018-07-24 12:42 ` M. Vefa Bicakci
2018-07-24 12:45 ` [PATCH v2] " M. Vefa Bicakci
2018-07-24 14:08 ` Boris Ostrovsky
2018-07-26 3:56 ` [PATCH v3] " M. Vefa Bicakci
2018-08-06 20:15 ` [PATCH v2] " Boris Ostrovsky
2018-08-06 20:16 ` Thomas Gleixner
2018-08-06 21:27 ` Boris Ostrovsky
2018-08-07 9:50 ` Ingo Molnar
2018-07-21 21:19 ` [PATCH 1/2] x86/entry/64: Do not clear %rbx under Xen Boris Ostrovsky
2018-07-21 23:18 ` M. Vefa Bicakci
2018-07-23 14:56 ` Boris Ostrovsky
2018-07-21 21:45 ` Andy Lutomirski
2018-07-21 23:19 ` M. Vefa Bicakci
2018-07-21 23:30 ` Andy Lutomirski
2018-07-21 23:37 ` M. Vefa Bicakci
2018-07-22 1:20 ` M. Vefa Bicakci
2018-07-22 17:56 ` Andy Lutomirski
2018-07-22 18:32 ` [Xen-devel] " Andrew Cooper
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