x86/paravirt/xen: Optimize pte_flags by marking it as paravirt_ident_[32|64] type.
Which means that we have to use:
__PV_IS_CALLEE_SAVE(_paravirt_ident_64)
which requires that the pte_flags on the 'pv_mmu_ops' structure
be defined as struct paravirt_callee_save. We end up using the
_paravirt_ident_64 function for both baremetal and for Xen guests
that have PAT disabled. For those that have pat_enabled, we end
up calling xen_pte_flags.
The big benefit of making the .pte_flags as struct paravirt_callee_save
and making it PTE_IDENT is that while the code looks as so when compiled:
ff 14 25 e8 52 c1 81 callq *0xffffffff81c152e8
That however, on baremetal and under Xen when !pat_enable ends up
being patched over (by using the DEF_NATIVE macro) to be:
48 89 f8 mov %rdi,%rax
66 66 66 90 data32 data32 xchg %ax,%ax
(the 32-bit version is of course different).
For details refer to 'paravirt_patch_ident_64' function.
The Xen version which requires pat_enable==1, ends up patched
to be:
call xen_pte_flags;
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
4 files changed
