Replace absolute references in inline asm with RIP-relative ones, to
avoid the need for relocation fixups at boot time. This is a
prerequisite for PIE linking, which only permits 64-bit wide
loader-visible absolute references.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/kernel/kvm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index df78ddee0abb..1a0335f328e1 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -807,8 +807,9 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
  * restoring to/from the stack.
  */
 #define PV_VCPU_PREEMPTED_ASM						     \
- "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"				     \
- "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
+ "0:leaq 0b(%rip), %rax\n\t"						     \
+ "addq   __per_cpu_offset - 0b(%rax,%rdi,8), %rax\n\t"			     \
+ "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time-0b(%rax)\n\t" \
  "setne  %al\n\t"
 
 DEFINE_ASM_FUNC(__raw_callee_save___kvm_vcpu_is_preempted,
-- 
2.47.3

On Thu, Jan 08, 2026, Ard Biesheuvel wrote:
> Replace absolute references in inline asm with RIP-relative ones, to
> avoid the need for relocation fixups at boot time. This is a
> prerequisite for PIE linking, which only permits 64-bit wide
> loader-visible absolute references.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  arch/x86/kernel/kvm.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index df78ddee0abb..1a0335f328e1 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -807,8 +807,9 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
>   * restoring to/from the stack.
>   */
>  #define PV_VCPU_PREEMPTED_ASM						     \
> - "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"				     \
> - "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
> + "0:leaq 0b(%rip), %rax\n\t"						     \

Please use something other than '0' for the label, it took me forever (and looking
at disassembly) to realize "0b" was just a backwards label and not some fancy
syntax I didn't know.

It might also be worth calling out in the changelog that this function is called
across CPUs, e.g. from kvm_smp_send_call_func_ipi(), and thus can't use gs:
or any other "normal" method for accessing per-CPU data.

> + "addq   __per_cpu_offset - 0b(%rax,%rdi,8), %rax\n\t"			     \
> + "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time-0b(%rax)\n\t" \
>   "setne  %al\n\t"
>  
>  DEFINE_ASM_FUNC(__raw_callee_save___kvm_vcpu_is_preempted,
> -- 
> 2.47.3
>

On Tue, 20 Jan 2026 09:04:26 -0800
Sean Christopherson <seanjc@google.com> wrote:

> On Thu, Jan 08, 2026, Ard Biesheuvel wrote:
> > Replace absolute references in inline asm with RIP-relative ones, to
> > avoid the need for relocation fixups at boot time. This is a
> > prerequisite for PIE linking, which only permits 64-bit wide
> > loader-visible absolute references.
> > 
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  arch/x86/kernel/kvm.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index df78ddee0abb..1a0335f328e1 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -807,8 +807,9 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
> >   * restoring to/from the stack.
> >   */
> >  #define PV_VCPU_PREEMPTED_ASM						     \
> > - "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"				     \
> > - "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
> > + "0:leaq 0b(%rip), %rax\n\t"						     \  
> 
> Please use something other than '0' for the label, it took me forever (and looking
> at disassembly) to realize "0b" was just a backwards label and not some fancy
> syntax I didn't know.

I remember taking a while to grok that as well.

Can't you just use . as in:
	leaq	.(%rip), %rax

shame the assembler doesn't understand:
	movq	%rip, %rax
(maybe it does...)

	David

On Tue, 20 Jan 2026 at 20:44, David Laight <david.laight.linux@gmail.com> wrote:
>
> On Tue, 20 Jan 2026 09:04:26 -0800
> Sean Christopherson <seanjc@google.com> wrote:
>
> > On Thu, Jan 08, 2026, Ard Biesheuvel wrote:
> > > Replace absolute references in inline asm with RIP-relative ones, to
> > > avoid the need for relocation fixups at boot time. This is a
> > > prerequisite for PIE linking, which only permits 64-bit wide
> > > loader-visible absolute references.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > ---
> > >  arch/x86/kernel/kvm.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > > index df78ddee0abb..1a0335f328e1 100644
> > > --- a/arch/x86/kernel/kvm.c
> > > +++ b/arch/x86/kernel/kvm.c
> > > @@ -807,8 +807,9 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
> > >   * restoring to/from the stack.
> > >   */
> > >  #define PV_VCPU_PREEMPTED_ASM                                                   \
> > > - "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"                                   \
> > > - "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
> > > + "0:leaq 0b(%rip), %rax\n\t"                                                    \
> >
> > Please use something other than '0' for the label, it took me forever (and looking
> > at disassembly) to realize "0b" was just a backwards label and not some fancy
> > syntax I didn't know.
>
> I remember taking a while to grok that as well.
>
> Can't you just use . as in:
>         leaq    .(%rip), %rax
>

How would the other two instructions referring to '0b' in their
immediates refer to '.' in that case?

On Tue, 20 Jan 2026 21:54:30 +0100
Ard Biesheuvel <ardb@kernel.org> wrote:

> On Tue, 20 Jan 2026 at 20:44, David Laight <david.laight.linux@gmail.com> wrote:
> >
> > On Tue, 20 Jan 2026 09:04:26 -0800
> > Sean Christopherson <seanjc@google.com> wrote:
> >  
> > > On Thu, Jan 08, 2026, Ard Biesheuvel wrote:  
> > > > Replace absolute references in inline asm with RIP-relative ones, to
> > > > avoid the need for relocation fixups at boot time. This is a
> > > > prerequisite for PIE linking, which only permits 64-bit wide
> > > > loader-visible absolute references.
> > > >
> > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > ---
> > > >  arch/x86/kernel/kvm.c | 5 +++--
> > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > > > index df78ddee0abb..1a0335f328e1 100644
> > > > --- a/arch/x86/kernel/kvm.c
> > > > +++ b/arch/x86/kernel/kvm.c
> > > > @@ -807,8 +807,9 @@ extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
> > > >   * restoring to/from the stack.
> > > >   */
> > > >  #define PV_VCPU_PREEMPTED_ASM                                                   \
> > > > - "movq   __per_cpu_offset(,%rdi,8), %rax\n\t"                                   \
> > > > - "cmpb   $0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax)\n\t" \
> > > > + "0:leaq 0b(%rip), %rax\n\t"                                                    \  
> > >
> > > Please use something other than '0' for the label, it took me forever (and looking
> > > at disassembly) to realize "0b" was just a backwards label and not some fancy
> > > syntax I didn't know.  
> >
> > I remember taking a while to grok that as well.
> >
> > Can't you just use . as in:
> >         leaq    .(%rip), %rax
> >  
> 
> How would the other two instructions referring to '0b' in their
> immediates refer to '.' in that case?

I'd forgotten about those, not in the quoted bit of patch :-(

Traditionally (going back to MACRO-11) numeric labels would start at 10
and go up in 10s, TECO had a nice macro to renumber them.
(Showing my age again)

	David