[PATCH v2] KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

[PATCH v2] KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

[Will Deacon]

Currently, it is not necessary for __finalise_el2() to configure
TPIDR_EL2:

* The hyp stub code does not consume the value of TPIDR_EL2.

* On the boot cpu, TPIDR_EL1 is used for the percpu offset until the
  ARM64_HAS_VIRT_HOST_EXTN cpucap is detected and boot alternatives
  are patched. Before boot alternatives are patched,
  cpu_copy_el2regs() will copy TPIDR_EL1 into TPIDR_EL2. It is not
  necessary for __finalise_el2() to initialise TPIDR_EL2 before this.

* Secondary CPUs are brought up after boot alternatives have been
  patched, and __secondary_switched() will initialize TPIDR_EL2 in
  'init_cpu_task', after finalise_el2() calls __finalise_el2()

* KVM hyp code which may consume TPIDR_EL2 is brought up after all
  secondaries have been booted, once TPIDR_El2 has been configured on
  all CPUs.

Remove the redundant initialisation from __finalise_el2().

Cc: Oliver Upton <oupton@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---

v2: Use Mark's commit message, add his R-b tag, rebase onto -rc4.
Link to v1: https://lore.kernel.org/r/20260330152927.26300-1-will@kernel.org

 arch/arm64/kernel/hyp-stub.S | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 634ddc904244..37c6976e44a4 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -104,11 +104,9 @@ SYM_CODE_START_LOCAL(__finalise_el2)
 	mov_q	x0, HCR_HOST_VHE_FLAGS
 	msr_hcr_el2 x0
 
-	// Use the EL1 allocated stack, per-cpu offset
+	// Use the EL1 allocated stack
 	mrs	x0, sp_el1
 	mov	sp, x0
-	mrs	x0, tpidr_el1
-	msr	tpidr_el2, x0
 
 	// FP configuration, vectors
 	mrs_s	x0, SYS_CPACR_EL12
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH v2] KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

[Marc Zyngier]

On Mon, 18 May 2026 16:31:26 +0100,
Will Deacon <will@kernel.org> wrote:
> 
> Currently, it is not necessary for __finalise_el2() to configure
> TPIDR_EL2:
> 
> * The hyp stub code does not consume the value of TPIDR_EL2.
> 
> * On the boot cpu, TPIDR_EL1 is used for the percpu offset until the
>   ARM64_HAS_VIRT_HOST_EXTN cpucap is detected and boot alternatives
>   are patched. Before boot alternatives are patched,
>   cpu_copy_el2regs() will copy TPIDR_EL1 into TPIDR_EL2. It is not
>   necessary for __finalise_el2() to initialise TPIDR_EL2 before this.
> 
> * Secondary CPUs are brought up after boot alternatives have been
>   patched, and __secondary_switched() will initialize TPIDR_EL2 in
>   'init_cpu_task', after finalise_el2() calls __finalise_el2()
> 
> * KVM hyp code which may consume TPIDR_EL2 is brought up after all
>   secondaries have been booted, once TPIDR_El2 has been configured on
>   all CPUs.
> 
> Remove the redundant initialisation from __finalise_el2().
> 
> Cc: Oliver Upton <oupton@kernel.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Will Deacon <will@kernel.org>

Reviewed-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v2] KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

[Marc Zyngier]

On Mon, 18 May 2026 16:39:30 +0100,
Marc Zyngier <maz@kernel.org> wrote:
> 
> On Mon, 18 May 2026 16:31:26 +0100,
> Will Deacon <will@kernel.org> wrote:
> > 
> > Currently, it is not necessary for __finalise_el2() to configure
> > TPIDR_EL2:
> > 
> > * The hyp stub code does not consume the value of TPIDR_EL2.
> > 
> > * On the boot cpu, TPIDR_EL1 is used for the percpu offset until the
> >   ARM64_HAS_VIRT_HOST_EXTN cpucap is detected and boot alternatives
> >   are patched. Before boot alternatives are patched,
> >   cpu_copy_el2regs() will copy TPIDR_EL1 into TPIDR_EL2. It is not
> >   necessary for __finalise_el2() to initialise TPIDR_EL2 before this.
> > 
> > * Secondary CPUs are brought up after boot alternatives have been
> >   patched, and __secondary_switched() will initialize TPIDR_EL2 in
> >   'init_cpu_task', after finalise_el2() calls __finalise_el2()
> > 
> > * KVM hyp code which may consume TPIDR_EL2 is brought up after all
> >   secondaries have been booted, once TPIDR_El2 has been configured on
> >   all CPUs.
> > 
> > Remove the redundant initialisation from __finalise_el2().
> > 
> > Cc: Oliver Upton <oupton@kernel.org>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: Will Deacon <will@kernel.org>
> 
> Reviewed-by: Marc Zyngier <maz@kernel.org>

Ah, realised too late you intended for this to go via the KVM tree.

I'll queue that for 7.2.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v2] KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

[Will Deacon]

On Mon, May 18, 2026 at 04:41:15PM +0100, Marc Zyngier wrote:
> On Mon, 18 May 2026 16:39:30 +0100,
> Marc Zyngier <maz@kernel.org> wrote:
> > 
> > On Mon, 18 May 2026 16:31:26 +0100,
> > Will Deacon <will@kernel.org> wrote:
> > > 
> > > Currently, it is not necessary for __finalise_el2() to configure
> > > TPIDR_EL2:
> > > 
> > > * The hyp stub code does not consume the value of TPIDR_EL2.
> > > 
> > > * On the boot cpu, TPIDR_EL1 is used for the percpu offset until the
> > >   ARM64_HAS_VIRT_HOST_EXTN cpucap is detected and boot alternatives
> > >   are patched. Before boot alternatives are patched,
> > >   cpu_copy_el2regs() will copy TPIDR_EL1 into TPIDR_EL2. It is not
> > >   necessary for __finalise_el2() to initialise TPIDR_EL2 before this.
> > > 
> > > * Secondary CPUs are brought up after boot alternatives have been
> > >   patched, and __secondary_switched() will initialize TPIDR_EL2 in
> > >   'init_cpu_task', after finalise_el2() calls __finalise_el2()
> > > 
> > > * KVM hyp code which may consume TPIDR_EL2 is brought up after all
> > >   secondaries have been booted, once TPIDR_El2 has been configured on
> > >   all CPUs.
> > > 
> > > Remove the redundant initialisation from __finalise_el2().
> > > 
> > > Cc: Oliver Upton <oupton@kernel.org>
> > > Cc: Marc Zyngier <maz@kernel.org>
> > > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > > Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> > > Signed-off-by: Will Deacon <will@kernel.org>
> > 
> > Reviewed-by: Marc Zyngier <maz@kernel.org>
> 
> Ah, realised too late you intended for this to go via the KVM tree.
> 
> I'll queue that for 7.2.

Thanks, Marc!

Will