Re: [PATCH 8/9] x86/virt/tdx: Exclude memory region hole within CMR as TDMR's reserved area

Huang, Kai
2024-06-18T00:12:55Z

On 17/06/2024 10:54 pm, Chao Gao wrote:
>> +/* Return whether a given region [start, end) is a sub-region of any CMR */
>> +static bool is_cmr_subregion(struct tdx_sysinfo_cmr_info *cmr_info, u64 start,
>> + u64 end)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < cmr_info->num_cmrs; i++) {
>> + u64 cmr_base = cmr_info->cmr_base[i];
>> + u64 cmr_size = cmr_info->cmr_size[i];
>> +
>> + if (start >= cmr_base && end <= (cmr_base + cmr_size))
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> /*
>> * Go through @tmb_list to find holes between memory areas. If any of
>
> The logic here is:
> 1. go through @tmb_list to find holes
> 2. skip a hole if it is in CMRs
>
> I am wondering if the kernel can traverse CMRs directly to find holes. This
> way, the new is_cmr_subregion() can be removed. And @tmb_list can be dropped
> from a few functions e.g., tdmr_populate_rsvd_holes/areas/areas_all(). So, this
> will simplify those functions a bit.

Traversing CMRs to find reserved areas for a given TDMR sounds good to
me logically. The whole construct_tdmrs() assumes all TDX memory blocks
are fully covered by CMRs anyway.

I'll try this out (validation is a bit tricky because we cannot
reproduce this issue internally).

>
>> * those holes fall within @tdmr, set up a TDMR reserved area to cover
>> @@ -835,7 +932,8 @@ static int tdmr_add_rsvd_area(struct tdmr_info *tdmr, int *p_idx, u64 addr,
>> static int tdmr_populate_rsvd_holes(struct list_head *tmb_list,
>> struct tdmr_info *tdmr,
>> int *rsvd_idx,
>> - u16 max_reserved_per_tdmr)
>> + u16 max_reserved_per_tdmr,
>> + struct tdx_sysinfo_cmr_info *cmr_info)
>
> Maybe this function can accept a pointer to tdx_sysinfo and remove
> @max_reserved_per_tdmr and @cmr_info because they are both TDX metadata and
> have only one possible combination for a given TDX module. Anyway, I don't have
> a strong opinion on this.

There are pros/cons of the two options. Passing the @cmr_info and
@max_reserved_per_tdmr makes this function more clear that it _exactly_
requires these two. Since passing a single @tdx_sysinfo doesn't reduce
the function arguments a lot (only one argument, and you have to get the
two inside the function anyway), I would keep the current way unless I
hear from something different from others.