x86/hvm: Propagate real error information up through hvm_load()

x86/hvm: Propagate real error information up through hvm_load()

hvm_load() is currently a mix of -errno and -1 style error handling, which
aliases -EPERM.  This leads to the following confusing diagnostics:

From userspace:
  xc: info: Restoring domain
  xc: error: Unable to restore HVM context (1 = Operation not permitted): Internal error
  xc: error: Restore failed (1 = Operation not permitted): Internal error
  xc_domain_restore: [1] Restore failed (1 = Operation not permitted)

From Xen:
  (XEN) HVM10.0 restore: inconsistent xsave state (feat=0x2ff accum=0x21f xcr0=0x7 bv=0x3 err=-22)
  (XEN) HVM10 restore: failed to load entry 16/0

The actual error was a bad backport, but the -EINVAL got converted to -EPERM
on the way out of the hypercall.

The overwhelming majority of *_load() handlers already use -errno consistenty.
Fix up the rest to be consistent, and fix a few other errors noticed along the
way.

 * Failures of hvm_load_entry() indicate a truncated record or other bad data
   size.  Use -ENODATA.
 * Don't use {g,}dprintk().  Omitting diagnostics in release builds is rude,
   and almost everything uses unconditional printk()'s.
 * Switch some errors for more appropriate ones.

Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 96e5ad4c476e70688295b3cfb537847a3351d6fd
master date: 2021-07-19 14:34:38 +0100