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SubjectRe: [PATCH v2] x86/hyper-v: Mark TLFS structures packed
> On Nov 30, 2018, at 4:54 AM, Vitaly Kuznetsov <> wrote:
> The TLFS structures are used for hypervisor-guest communication and must
> exactly meet the specification.
> Compilers can add alignment padding to structures or reorder struct members
> for randomization and optimization, which would break the hypervisor ABI.
> Mark the structures as packed to prevent this.

Seems good to me (I made sure you remembered to set __packed for the nested
structs ;-) )

If needed:

Acked-by: Nadav Amit <>

Having said that, something else is sort of strange in the TLFS definitions,
I think (I really know little about this whole protocol). Look at the
following definitions from hyperv-tlfs.h:

> struct hv_vpset {
> u64 format;
> u64 valid_bank_mask;
> u64 bank_contents[];
> };
> struct hv_tlb_flush_ex {
> u64 address_space;
> u64 flags;
> struct hv_vpset hv_vp_set;
> u64 gva_list[];
> };

It seems you have two flexible array members at the end of hv_tlb_flush_ex.
This causes bank_contents[x] and gva_list[x] to overlap. So unless they have
the same meaning, this asks for trouble IMHO.

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