Re: [kvm-unit-tests PATCH v6 4/4] x86: Add test case for INVVPID with LAM

[Sean Christopherson <seanjc@google.com>]

On Mon, Jan 22, 2024, Binbin Wu wrote:
> +	if (this_cpu_has(X86_FEATURE_LA57) && read_cr4() & X86_CR4_LA57)

Checking for feature support seems superfluous, e.g. LA57 should never be set if
it's unsupported.  Then you can do

	lam_mask = is_la57_enabled() ? LAM57_MASK : LAM48_MASK;

> +		lam_mask = LAM57_MASK;
> +
> +	vaddr = alloc_vpage();
> +	install_page(current_page_table(), virt_to_phys(alloc_page()), vaddr);
> +	/*
> +	 * Since the stack memory address in KUT doesn't follow kernel address
> +	 * space partition rule, reuse the memory address for descriptor and
> +	 * the target address in the descriptor of invvpid.
> +	 */
> +	operand = (struct invvpid_operand *)vaddr;

Why bother backing the virtual address?  MOV needs a valid translation, but
INVVPID does not (ditto for INVLPG and INVPCID, though it might be simpler and
easier to just use the allocated address for those).

> +	operand->vpid = 0xffff;
> +	operand->gla = (u64)vaddr;
> +	operand = (struct invvpid_operand *)set_la_non_canonical((u64)operand,
> +								 lam_mask);
> +	fault = test_for_exception(GP_VECTOR, ds_invvpid, operand);
> +	report(!fault, "INVVPID (LAM on): tagged operand");