Messages in this thread | | | From | Uros Bizjak <> | Date | Tue, 21 Nov 2023 10:29:16 +0100 | Subject | Re: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address |
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On Tue, Nov 21, 2023 at 10:05 AM Kirill A. Shutemov <kirill@shutemov.name> wrote: > > On Mon, Nov 20, 2023 at 08:58:29PM +0100, Uros Bizjak wrote: > > On Mon, Nov 20, 2023 at 6:15 PM Borislav Petkov <bp@alien8.de> wrote: > > > > > > On Mon, Nov 20, 2023 at 04:33:50PM +0100, Uros Bizjak wrote: > > > > The "a" asm operand modifier substitutes a memory reference, with the > > > > actual operand treated as address. For x86_64, when a symbol is > > > > provided, the "a" modifier emits "sym(%rip)" instead of "sym". > > > > > > > > Clang allows only "i" and "r" operand constraints with an "a" modifier, > > > > so the patch normalizes the modifier/constraint pair to "a"/"i" > > > > > > s/the patch normalizes/normalize/ > > > > > > > which is consistent between both compilers. > > > > > > > > No functional change intended. > > > > > > > > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> > > > > Cc: Dave Hansen <dave.hansen@linux.intel.com> > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > > Cc: Peter Zijlstra <peterz@infradead.org> > > > > Cc: Thomas Gleixner <tglx@linutronix.de> > > > > Cc: Ingo Molnar <mingo@kernel.org> > > > > Cc: Borislav Petkov <bp@alien8.de> > > > > Cc: "H. Peter Anvin" <hpa@zytor.com> > > > > Signed-off-by: Uros Bizjak <ubizjak@gmail.com> > > > > --- > > > > arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------ > > > > 1 file changed, 4 insertions(+), 12 deletions(-) > > > > > > > > diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c > > > > index d73aeb16417f..6a351fdd1b39 100644 > > > > --- a/arch/x86/mm/mem_encrypt_identity.c > > > > +++ b/arch/x86/mm/mem_encrypt_identity.c > > > > @@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp) > > > > * We're running identity mapped, so we must obtain the address to the > > > > * SME encryption workarea using rip-relative addressing. > > > > */ > > > > - asm ("lea sme_workarea(%%rip), %0" > > > > - : "=r" (workarea_start) > > > > - : "p" (sme_workarea)); > > > > + asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea)); > > > > > > Yeah, I saw that particular subthread today. > > > > > > Are you sure this "a" modifier DTRT with all gcc version we support? > > > > > > I.e., from 5.1 onwards... > > > > Yes [1]. > > > > [1] https://godbolt.org/z/aWe7b16rT > > But Clang generates RIP-relative load only starting from version 15. > Clange 11 claimed to be supported.
Huh, what a bummer...
The patch is retracted then.
Thanks, Uros.
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