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    SubjectRe: [PATCH v7 16/20] x86/virt/tdx: Configure TDX module with TDMRs and global KeyID
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    On 11/24/22 16:59, Huang, Kai wrote:
    > On Wed, 2022-11-23 at 15:56 -0800, Dave Hansen wrote:
    >> On 11/20/22 16:26, Kai Huang wrote:
    >>> + array_sz = ALIGN(tdmr_num * sizeof(u64), TDMR_INFO_PA_ARRAY_ALIGNMENT);
    >>> + tdmr_pa_array = kzalloc(array_sz, GFP_KERNEL);
    >>
    >> Just to be clear, all that chatter about alignment is because the
    >> *START* of the array has to be aligned. Right?
    >
    > Correct.
    >
    >> I see alignment for
    >> 'array_sz', but that's not the start of the array.
    >>
    >> tdmr_pa_array is the start of the array. Where is *THAT* aligned?
    >
    > The alignment is assumed to be guaranteed based on the Documentation you quoted
    > below.

    I'm feeling kinda dense today, being Thanksgiving and all. Could you
    please walk me through, step-by-step how you get kzalloc() to give you
    an allocation where the start address is 512-byte aligned?

    ...
    > Perhaps I should just allocate one page so it must be 512-byte aligned?
    >
    > /*
    > * TDMR_INFO entries are configured to the TDX module via an array
    > * of physical address of each TDMR_INFO. The TDX module requires
    > * the array itself to be 512-byte aligned. Just allocate a page
    > * to use it as the array so the alignment can be guaranteed. The
    > * page will be freed after TDH.SYS.CONFIG anyway.
    > */

    Kai, I just plain can't believe at this point that comments like this
    are still being written. I _thought_ I was very clear before that if
    you have a constant, say:

    #define FOO_ALIGN 512

    and you want to align foo, you can just do:

    foo = ALIGN(foo, FOO_ALIGN);

    You don't need to mention the 512-byte alignment again. The #define is
    good enough.


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