On Wed, Feb 14, 2018 at 5:55 PM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > On Wed, Feb 14, 2018 at 05:22:58PM +0000, Andy Lutomirski wrote: >> On Wed, Feb 14, 2018 at 11:16 AM, Kirill A. Shutemov >> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: >> > For boot-time switching between paging modes, we need to be able to >> > adjust virtual mask shifts. >> > >> > The change doesn't affect the kernel image size much: >> > >> > text data bss dec hex filename >> > 8628892 4734340 1368064 14731296 e0c820 vmlinux.before >> > 8628966 4734340 1368064 14731370 e0c86a vmlinux.after >> > >> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> >> > --- >> > arch/x86/entry/entry_64.S | 12 ++++++++++++ >> > arch/x86/include/asm/page_64_types.h | 2 +- >> > arch/x86/mm/dump_pagetables.c | 12 ++++++++++-- >> > arch/x86/mm/kaslr.c | 4 +++- >> > 4 files changed, 26 insertions(+), 4 deletions(-) >> > >> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> > index cd216c9431e1..1608b13a0b36 100644 >> > --- a/arch/x86/entry/entry_64.S >> > +++ b/arch/x86/entry/entry_64.S >> > @@ -260,8 +260,20 @@ GLOBAL(entry_SYSCALL_64_after_hwframe) >> > * Change top bits to match most significant bit (47th or 56th bit >> > * depending on paging mode) in the address. >> > */ >> > +#ifdef CONFIG_X86_5LEVEL >> > + testl $1, pgtable_l5_enabled(%rip) >> > + jz 1f >> > + shl $(64 - 57), %rcx >> > + sar $(64 - 57), %rcx >> > + jmp 2f >> > +1: >> > + shl $(64 - 48), %rcx >> > + sar $(64 - 48), %rcx >> > +2: >> > +#else >> > shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx >> > sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx >> > +#endif >> >> Eww. >> >> Can't this be ALTERNATIVE "shl ... sar ...", "shl ... sar ...", >> X86_FEATURE_5LEVEL or similar? > > Optimization comes in a separate patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/commit/?h=la57/boot-switching/wip&id=015fa3576a7f2b8bd271096bb3a12b06cdc845af > Nice! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
