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    SubjectRe: How could we get rid of saved_max_pfn for calgary iommu?
    Remove muli@il.ibm.com from CC, this email isn't valid now.

    On 02/19/14 at 09:36pm, Vivek Goyal wrote:
    > On Wed, Feb 19, 2014 at 05:04:22PM -0700, Jon Mason wrote:
    > > On Tue, Feb 18, 2014 at 11:18 PM, WANG Chao <chaowang@redhat.com> wrote:
    > > > Hi, All
    > > >
    > > > arch/x86/kernel/pci-calgary.c is the only user of saved_max_pfn today:
    > > >
    > > > int __init detect_calgary(void)
    > > > {
    > > > [..]
    > > > specified_table_size = determine_tce_table_size((is_kdump_kernel() ?
    > > > saved_max_pfn : max_pfn) * PAGE_SIZE);
    > > > [..]
    > > > }
    > >
    > > IIUC, the purpose of this code is to reuse the TCE table from the
    > > previous kernel. Thus, it needs to be of the same size as the
    > > pre-kdump kernel. It is using the max_pfn to determine the TCE table
    > > size in the non-kdump case. If there is another way to determine the
    > > size it used before, then I am fine making the change to use that way.
    >
    > How about passing old tce table size on command line to second kernel.
    > Given the fact that it is specific to calgary only, we can it very
    > specific. Say calgary_iommu_old_tce_table_sz=<size>.

    Don't need to introduce a new parameter, this is already there:
    calgary=[64k,128k,256k,512k,1M,2M,4M,8M]

    >
    > But we will then need to know the size of TCE table in first kernel. Is
    > this information exported to user space somewhere?

    If this value isn't exported to userspace or even won't in the future, I think
    the table size also can be determined by userspace. We can implement something like the
    kernel does in kexec.

    The calgary code:

    static inline int __init determine_tce_table_size(u64 ram)
    {
    int ret;

    if (specified_table_size != TCE_TABLE_SIZE_UNSPECIFIED)
    return specified_table_size;

    /*
    * Table sizes are from 0 to 7 (TCE_TABLE_SIZE_64K to
    * TCE_TABLE_SIZE_8M). Table size 0 has 8K entries and each
    * larger table size has twice as many entries, so shift the
    * max ram address by 13 to divide by 8K and then look at the
    * order of the result to choose between 0-7.
    */
    ret = get_order(ram >> 13);
    if (ret > TCE_TABLE_SIZE_8M)
    ret = TCE_TABLE_SIZE_8M;

    return ret;
    }

    But it still no clear to me how I can determine calgary iommu is in use in 1st kernel.

    Thanks
    WANG Chao


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