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KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

PATCH Applied Will Deacon 2 participants 5 messages May 18 – May 27

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Will Deacon

author maintainer
#0 lore raw

PATCH v2 1/1 KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

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 <[email protected]>
Cc Marc Zyngier <[email protected]>
Cc Catalin Marinas <[email protected]>
Reviewed-by Mark Rutland <[email protected]>
Signed-off-by Will Deacon <[email protected]>

---

v2: Use Mark's commit message, add his R-b tag, rebase onto -rc4. Link to v1: https://lore.kernel.org/r/[email protected]

 arch/arm64/kernel/hyp-stub.S | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)
arch/arm64/kernel/hyp-stub.S +1 -3
index 634ddc904244..37c6976e44a4 100644
@@ -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
Signature · 1 line
2.54.0.563.g4f69b47b94-goog
maintainer Reviewed-by on v2 1/1
#1 lore raw
Quoted 20 lines · 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.

Quoted 7 lines

Remove the redundant initialisation from __finalise_el2().

Cc Oliver Upton <[email protected]>
Cc Marc Zyngier <[email protected]>
Cc Catalin Marinas <[email protected]>
Reviewed-by Mark Rutland <[email protected]>
Signed-off-by Will Deacon <[email protected]>
Reviewed-by Marc Zyngier <[email protected]>
	M.
Signature · 1 line
Without deviation from the norm, progress is not possible.
maintainer
#2 lore raw
Quoted 25 lines · Marc Zyngier
Quoted 22 lines · 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().

Quoted 7 lines
Quoted 5 lines
Cc Oliver Upton <[email protected]>
Cc Marc Zyngier <[email protected]>
Cc Catalin Marinas <[email protected]>
Reviewed-by Mark Rutland <[email protected]>
Signed-off-by Will Deacon <[email protected]>
Reviewed-by Marc Zyngier <[email protected]>

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

I'll queue that for 7.2.

Thanks,

	M.
Signature · 1 line
Without deviation from the norm, progress is not possible.
author maintainer
#3 lore raw
Quoted 33 lines · Marc Zyngier
Quoted 31 lines · Marc Zyngier
Quoted 27 lines · 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 <[email protected]>
Cc Marc Zyngier <[email protected]>
Cc Catalin Marinas <[email protected]>
Reviewed-by Mark Rutland <[email protected]>
Signed-off-by Will Deacon <[email protected]>
Quoted 5 lines
Quoted 1 line
Reviewed-by Marc Zyngier <[email protected]>

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

I'll queue that for 7.2.

Thanks, Marc!

Will

maintainer Applied
#4 lore raw
In reply to Will Deacon
Quoted 5 lines · 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.

Quoted 7 lines

* 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.

[...]

Applied to next, thanks!

[1/1] KVM: arm64: Don't populate TPIDR_EL2 in finalise_el2()

      commit: 4cceeb8da363ac5127b147ee7345104743f53e9d

Cheers,

	M.
Signature · 1 line
Without deviation from the norm, progress is not possible.