Re: [RFC PATCH v4 22/36] i386/tdx: Track RAM entries for TDX VM

[Isaku Yamahata]

On Thu, May 26, 2022 at 03:33:10PM +0800,
Xiaoyao Li <xiaoyao.li@intel.com> wrote:

> On 5/24/2022 3:37 PM, Gerd Hoffmann wrote:
> > I think all this can be simplified, by
> >    (1) Change the existing entry to cover the accepted ram range.
> >    (2) If there is room before the accepted ram range add a
> >        TDX_RAM_UNACCEPTED entry for that.
> >    (3) If there is room after the accepted ram range add a
> >        TDX_RAM_UNACCEPTED entry for that.
> 
> I implement as below. Please help review.
> 
> +static int tdx_accept_ram_range(uint64_t address, uint64_t length)
> +{
> +    uint64_t head_start, tail_start, head_length, tail_length;
> +    uint64_t tmp_address, tmp_length;
> +    TdxRamEntry *e;
> +    int i;
> +
> +    for (i = 0; i < tdx_guest->nr_ram_entries; i++) {
> +        e = &tdx_guest->ram_entries[i];
> +
> +        if (address + length < e->address ||
> +            e->address + e->length < address) {
> +                continue;
> +        }
> +
> +        /*
> +         * The to-be-accepted ram range must be fully contained by one
> +         * RAM entries
> +         */
> +        if (e->address > address ||
> +            e->address + e->length < address + length) {
> +            return -EINVAL;
> +        }
> +
> +        if (e->type == TDX_RAM_ADDED) {
> +            return -EINVAL;
> +        }
> +
> +        tmp_address = e->address;
> +        tmp_length = e->length;
> +
> +        e->address = address;
> +        e->length = length;
> +        e->type = TDX_RAM_ADDED;
> +
> +        head_length = address - tmp_address;
> +        if (head_length > 0) {
> +            head_start = e->address;
> +            tdx_add_ram_entry(head_start, head_length, TDX_RAM_UNACCEPTED);

tdx_add_ram_entry() increments tdx_guest->nr_ram_entries.  I think it's worth
for comments why this is safe regarding to this for-loop.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>