Re: Problem with IOMEM and domain reboot

[Oleksandr Andrushchenko <andr2000@gmail.com>]

On 02/06/2018 02:52 PM, Wei Liu wrote:
> On Tue, Feb 06, 2018 at 02:44:56PM +0200, Oleksandr Andrushchenko wrote:
>>   From aa1f20af73a5a3c8f2c904b857a79334d18d41ff Mon Sep 17 00:00:00 2001
>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>> Date: Wed, 20 Dec 2017 17:51:18 +0200
>>>> Subject: [PATCH] [HACK] Reset iomem's gfn to LIBXL_INVALID_GFN on reboot
>>>>
>>>> During domain reboot its configuration is partially reused
>>>> to re-create a new domain, but iomem's GFN field for the
>>>> iomem is only restored for those memory ranges, which are
>>>> configured in form of [IOMEM_START,NUM_PAGES[@GFN], but not for
>>>> those in form of [IOMEM_START,NUM_PAGES], e.g. without GFN.
>>>> For the latter GFN is reset to 0, but while mapping ranges
>>>> to a domain during reboot there is a check that GFN treated
>>>> as valid if it is not equal to LIBXL_INVALID_GFN, thus making
>>>> Xen to map IOMEM_START to address 0 in the guest's address space.
>>>>
>>>> Workaround it by resseting GFN to LIBXL_INVALID_GFN, so xl
>>>> can set proper values for mapping on reboot.
>>>>
>>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>> ---
>>>>    tools/libxl/libxl_domain.c | 9 +++++++++
>>>>    1 file changed, 9 insertions(+)
>>>>
>>>> diff --git a/tools/libxl/libxl_domain.c b/tools/libxl/libxl_domain.c
>>>> index ef1a0927b00d..2678ad2ad54f 100644
>>>> --- a/tools/libxl/libxl_domain.c
>>>> +++ b/tools/libxl/libxl_domain.c
>>>> @@ -1647,6 +1647,15 @@ int libxl_retrieve_domain_configuration(libxl_ctx *ctx, uint32_t domid,
>>>>            }
>>>>        }
>>>> +    /* reset IOMEM's GFN to initial value */
>>>> +    {
>>>> +        int i;
>>>> +
>>>> +        for (i = 0; i < d_config->b_info.num_iomem; i++)
>>>> +            if (d_config->b_info.iomem[i].gfn == 0)
>>>> +                d_config->b_info.iomem[i].gfn = LIBXL_INVALID_GFN;
>>>> +    }
>>>> +
>>> I don't think this is necessary. Instead we should tell libxl to save
>>> the generated value into the template. Add an update_config hook for the
>>> iomem type should be better.
>> Agree, this is why I tagged the patch as [HACK]
>> Unfortunately, I have little knowledge of libxl and not sure
>> how to properly fix it. Can you tell a bit more on what
>> a proper fix could be?
> See libxl__update_domain_configuration, which is called after domain
> construction is completed. It will call the update_config hook for a
> device type to save anything that is generated in the process of domain
> creation. One example is in libxl_nic. You can do the same to iomem I
> think.
>
> The end result is the generated values you care about are saved into the
> template. When the domain is migrated / rebooted libxl will use the
> saved values instead.
Thank you, will look at it to make a proper fix
> Strictly speaking your patch of adding the snippet to
> libxl_retrieve_domain_configuration isn't wrong, but I would prefer that
> function to only contain code to fetch states that can be changed during
> domain runtime. The iomem range isn't one of those states AIUI.
>
> Wei.
>
>
>>> Wei.
>> Thank you,
>> Oleksandr


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel