x86/sgx: Move PTE zap code to new sgx_zap_enclave_ptes()

x86/sgx: Move PTE zap code to new sgx_zap_enclave_ptes()

[ Upstream commit f89c2f9bf5a64f619de06ded4349dff5a35da860 ]

The SGX reclaimer removes page table entries pointing to pages that are
moved to swap.

SGX2 enables changes to pages belonging to an initialized enclave, thus
enclave pages may have their permission or type changed while the page
is being accessed by an enclave. Supporting SGX2 requires page table
entries to be removed so that any cached mappings to changed pages
are removed. For example, with the ability to change enclave page types
a regular enclave page may be changed to a Thread Control Structure
(TCS) page that may not be accessed by an enclave.

Factor out the code removing page table entries to a separate function
sgx_zap_enclave_ptes(), fixing accuracy of comments in the process,
and make it available to the upcoming SGX2 code.

Place sgx_zap_enclave_ptes() with the rest of the enclave code in
encl.c interacting with the page table since this code is no longer
unique to the reclaimer.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/b010cdf01d7ce55dd0f00e883b7ccbd9db57160a.1652137848.git.reinette.chatre@intel.com
Stable-dep-of: 0d3e0dfd68fb ("x86/sgx: Fix size overflows in sgx_encl_create()")
Signed-off-by: Sasha Levin <sashal@kernel.org>