Re: [PATCH 07/25] KVM: TDX: Add helper functions to allocate/free TDX private host key id

[Paolo Bonzini]

On 8/13/24 00:48, Rick Edgecombe wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>
> Add helper functions to allocate/free TDX private host key id (HKID).
>
> The memory controller encrypts TDX memory with the assigned HKIDs. Each TDX
> guest must be protected by its own unique TDX HKID.
>
> The HW has a fixed set of these HKID keys. Out of those, some are set aside
> for use by for other TDX components, but most are saved for guest use. The
> code that does this partitioning, records the range chosen to be available
> for guest use in the tdx_guest_keyid_start and tdx_nr_guest_keyids
> variables.
>
> Use this range of HKIDs reserved for guest use with the kernel's IDA
> allocator library helper to create a mini TDX HKID allocator that can be
> called when setting up a TD. This way it can have an exclusive HKID, as is
> required. This allocator will be used in future changes.

This is basically what Dave was asking for, isn't it?

Paolo

> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
> uAPI breakout v1:
>   - Update the commit message
>   - Delete stale comment on global hkdi
>   - Deleted WARN_ON_ONCE() as it doesn't seemed very usefull
>
> v19:
>   - Removed stale comment in tdx_guest_keyid_alloc() by Binbin
>   - Update sanity check in tdx_guest_keyid_free() by Binbin
>
> v18:
>   - Moved the functions to kvm tdx from arch/x86/virt/vmx/tdx/
>   - Drop exporting symbols as the host tdx does.
> ---
>   arch/x86/kvm/vmx/tdx.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index dbcc1ed80efa..b1c885ce8c9c 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -14,6 +14,21 @@ static enum cpuhp_state tdx_cpuhp_state;
>   
>   static const struct tdx_sysinfo *tdx_sysinfo;
>   
> +/* TDX KeyID pool */
> +static DEFINE_IDA(tdx_guest_keyid_pool);
> +
> +static int __used tdx_guest_keyid_alloc(void)
> +{
> +	return ida_alloc_range(&tdx_guest_keyid_pool, tdx_guest_keyid_start,
> +			       tdx_guest_keyid_start + tdx_nr_guest_keyids - 1,
> +			       GFP_KERNEL);
> +}
> +
> +static void __used tdx_guest_keyid_free(int keyid)
> +{
> +	ida_free(&tdx_guest_keyid_pool, keyid);
> +}
> +
>   static int tdx_online_cpu(unsigned int cpu)
>   {
>   	unsigned long flags;