[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: issue with dom0_pvh on Xen 4.20
- To: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 2 Sep 2025 14:56:23 +0200
- Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Tue, 02 Sep 2025 12:56:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.09.2025 14:54, Manuel Bouyer wrote:
> On Tue, Sep 02, 2025 at 02:45:04PM +0200, Jan Beulich wrote:
>>>> What puzzles me is that:
>>>>
>>>> - %cr2 is 0, so probably the first fault wasn't a page fault
>>>
>>> AFAIK it can't be as we're still in real mode
>>
>> It's protected mode, but with paging still off.
>>
>>>> - RIP is %ebx + 8, so maybe the code was just clobbered by the loop?
>>>>
>>>> Could it be the code has been moved to this location, or is about to
>>>> be moved away afterwards?
>>>
>>> No. RIP shouldn't end up there in any way. the assembly code is quite
>>> simple,
>>> it's just a loop and I'm quite confident that we did enter the loop with
>>> sane values
>>
>> Yet Jürgen has a point - entry point and what is being modified are on the
>> same page (and despite paging still being off, you writing page tables here
>> makes pages a relevant unit). Considering
>> - entry point @ 0x20e4d0
>> - %ecx = 0xdfeb7
>> - %ebx = 0x20e260
>> the loop continuing a little further will overwrite the entry point code.
>> And with the entry point not at an even (e.g page-aligned) address, other
>> code (like the one here) could conceivably live immediately ahead of it.
>> (Of course this overwriting may be intentional, but it looks suspicious in
>> this context.)
>
> Indeed. Now the exact same kernel is booting fine with Xen 4.18 (and also
> the same bootstrap is used for domU PVH which works with Xen 4.20).
> I guess something changed in the way Xen sets up the dom0 kernel.
Hence why Andrew asked for full logs of both boots, to put side by side.
Jan
|
