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Date: Tue, 21 Nov 2023 12:00:41 +0300 From: "Kirill A. Shutemov" <kirill@...temov.name> To: Uros Bizjak <ubizjak@...il.com> Cc: Borislav Petkov <bp@...en8.de>, x86@...nel.org, linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address 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@...en8.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@...ux-foundation.org> > > > Cc: Dave Hansen <dave.hansen@...ux.intel.com> > > > Cc: Andy Lutomirski <luto@...nel.org> > > > Cc: Peter Zijlstra <peterz@...radead.org> > > > Cc: Thomas Gleixner <tglx@...utronix.de> > > > Cc: Ingo Molnar <mingo@...nel.org> > > > Cc: Borislav Petkov <bp@...en8.de> > > > Cc: "H. Peter Anvin" <hpa@...or.com> > > > Signed-off-by: Uros Bizjak <ubizjak@...il.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. -- Kiryl Shutsemau / Kirill A. Shutemov
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