x86/sgx: Drop racy follow_pfn() check

mainline inclusion
from mainline-v5.12-rc1-dontuse
commit dc9b7be5
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SIGI
CVE: NA

--------------------------------

PTE insertion is fundamentally racy, and this check doesn't do anything
useful. Quoting Sean:

  "Yeah, it can be whacked. The original, never-upstreamed code asserted
  that the resolved PFN matched the PFN being installed by the fault
  handler as a sanity check on the SGX driver's EPC management. The
  WARN assertion got dropped for whatever reason, leaving that useless
  chunk."

Jason stumbled over this as a new user of follow_pfn(), and I'm trying
to get rid of unsafe callers of that function so it can be locked down
further.

This is independent prep work for the referenced patch series:

  https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vetter@ffwll.ch/



Intel-SIG: commit dc9b7be5 x86/sgx: Drop racy follow_pfn() check
Backport for SGX Foundations support

Fixes: 947c6e11 ("x86/sgx: Add ptrace() support for the SGX driver")
Reported-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/20210204184519.2809313-1-daniel.vetter@ffwll.ch


Signed-off-by: Fan Du <fan.du@intel.com> #openEuler_contributor
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>
Reviewed-by: Bamvor Zhang <bamvor.zhang@suse.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>