Re: [PATCH 07/13] x86/virt/tdx: Add SEAMCALL wrapper tdh_mem_sept_add() to add SEPT pages

Edgecombe, Rick P
2025-01-02T22:00:06Z

On Wed, 2025-01-01 at 02:49 -0500, Paolo Bonzini wrote:
>
> +u64 tdh_mem_sept_add(struct tdx_td *td, u64 gpa, u64 level, u64 hpa, u64 *rcx, u64 *rdx)
> +{
> + struct tdx_module_args args = {
> + .rcx = gpa | level,

The bit packing here is a bit magic. Yan had been looking at adding a union like
below to use internally in tdh_mem_sept_add() to pack the rcx register.

union tdx_sept_gpa_mapping_info {
struct {
u64 level : 3;
u64 reserved1 : 9;
u64 gfn : 40;
u64 reserved2 : 12;
};
u64 full;
};

It might be a bit verbose, but I agree something should be done.

> + .rdx = tdx_tdr_pa(td),
> + .r8 = hpa,
> + };
> + u64 ret;
> +
> + clflush_cache_range(__va(hpa), PAGE_SIZE);
> + ret = seamcall_ret(TDH_MEM_SEPT_ADD, &args);
> +
> + *rcx = args.rcx;
> + *rdx = args.rdx;

This was changed to this:
*extended_err1 = args.rcx;
*extended_err2 = args.rdx;

The reasoning is rcx and rdx are not very clear names. The caller only uses them
for printing raw error codes, so don't bother creating a union or anything
fancy. The print statements should print the raw error code to help in debugging
situations where new bits are defined and returned by a future buggy TDX module.

> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(tdh_mem_sept_add);
> +
> u64 tdh_vp_addcx(struct tdx_vp *vp, struct page *tdcx_page)
> {
> struct tdx_module_args args = {
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index 62cb7832c42d..308d3aa565d7 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -16,6 +16,7 @@
> * TDX module SEAMCALL leaf functions
> */
> #define TDH_MNG_ADDCX 1
> +#define TDH_MEM_SEPT_ADD 3
> #define TDH_VP_ADDCX 4
> #define TDH_MNG_KEY_CONFIG 8
> #define TDH_MNG_CREATE 9