kaiser: use ALTERNATIVE instead of x86_cr3_pcid_noflush
authorHugh Dickins <hughd@google.com>
Wed, 4 Oct 2017 03:49:04 +0000 (20:49 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 5 Jan 2018 14:44:26 +0000 (15:44 +0100)
commit2dff99eb0335f9e0817410696a180dba25ca7371
treefb7268a2f4d63ac4e8080bc4b17fe628e250450a
parente405a064bd7d6eca88935342ddb71057a9d6ceab
kaiser: use ALTERNATIVE instead of x86_cr3_pcid_noflush

Now that we're playing the ALTERNATIVE game, use that more efficient
method: instead of user-mapping an extra page, and reading an extra
cacheline each time for x86_cr3_pcid_noflush.

Neel has found that __stringify(bts $X86_CR3_PCID_NOFLUSH_BIT, %rax)
is a working substitute for the "bts $63, %rax" in these ALTERNATIVEs;
but the one line with $63 in looks clearer, so let's stick with that.

Worried about what happens with an ALTERNATIVE between the jump and
jump label in another ALTERNATIVE?  I was, but have checked the
combinations in SWITCH_KERNEL_CR3_NO_STACK at entry_SYSCALL_64,
and it does a good job.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/x86/entry/entry_64.S
arch/x86/include/asm/kaiser.h
arch/x86/mm/kaiser.c