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KVM: arm64: Initialize HCR_EL2.E2H early

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On CPUs without FEAT_E2H0, HCR_EL2.E2H is RES1, but may reset to an
UNKNOWN value out of reset and consequently may not read as 1 unless it
has been explicitly initialized.

We handled this for the head.S boot code in commits:

  3944382fa6 ("arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is negative")
  b3320142f3 ("arm64: Fix early handling of FEAT_E2H0 not being implemented")

Unfortunately, we forgot to apply a similar fix to the KVM PSCI entry
points used when relaying CPU_ON, CPU_SUSPEND, and SYSTEM SUSPEND. When
KVM is entered via these entry points, the value of HCR_EL2.E2H may be
consumed before it has been initialized (e.g. by the 'init_el2_state'
macro).

Initialize HCR_EL2.E2H early in these paths such that it can be consumed
reliably. The existing code in head.S is factored out into a new
'init_el2_hcr' macro, and this is used in the __kvm_hyp_init_cpu()
function common to all the relevant PSCI entry points.

For clarity, I've tweaked the assembly used to check whether
ID_AA64MMFR4_EL1.E2H0 is negative. The bitfield is extracted as a signed
value, and this is checked with a signed-greater-or-equal (GE) comparison.

As the hyp code will reconfigure HCR_EL2 later in ___kvm_hyp_init(), all
bits other than E2H are initialized to zero in __kvm_hyp_init_cpu().

Fixes: 3944382fa6 ("arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is negative")
Fixes: b3320142f3 ("arm64: Fix early handling of FEAT_E2H0 not being implemented")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ahmed Genidi <ahmed.genidi@arm.com>
Cc: Ben Horgan <ben.horgan@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20250227180526.1204723-2-mark.rutland@arm.com
[maz: fixed LT->GE thinko]
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Mark Rutland 2025-02-27 18:05:25 +00:00 committed by Marc Zyngier
parent fa808ed4e1
commit 7a68b55ff3
3 changed files with 34 additions and 19 deletions
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26
arch/arm64/include/asm/el2_setup.h
View File

@ -16,6 +16,32 @@
#include <asm/sysreg.h>
#include <linux/irqchip/arm-gic-v3.h>
.macro init_el2_hcr val
mov_q x0, \val
/*
* Compliant CPUs advertise their VHE-onlyness with
* ID_AA64MMFR4_EL1.E2H0 < 0. On such CPUs HCR_EL2.E2H is RES1, but it
* can reset into an UNKNOWN state and might not read as 1 until it has
* been initialized explicitly.
*
* Fruity CPUs seem to have HCR_EL2.E2H set to RAO/WI, but
* don't advertise it (they predate this relaxation).
*
* Initalize HCR_EL2.E2H so that later code can rely upon HCR_EL2.E2H
* indicating whether the CPU is running in E2H mode.
*/
mrs_s x1, SYS_ID_AA64MMFR4_EL1
sbfx x1, x1, #ID_AA64MMFR4_EL1_E2H0_SHIFT, #ID_AA64MMFR4_EL1_E2H0_WIDTH
cmp x1, #0
b.ge .LnVHE_\@
orr x0, x0, #HCR_E2H
.LnVHE_\@:
msr hcr_el2, x0
isb
.endm
.macro __init_el2_sctlr
mov_q x0, INIT_SCTLR_EL2_MMU_OFF
msr sctlr_el2, x0

19
arch/arm64/kernel/head.S
View File

@ -298,25 +298,8 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
msr sctlr_el2, x0
isb
0:
mov_q x0, HCR_HOST_NVHE_FLAGS
/*
* Compliant CPUs advertise their VHE-onlyness with
* ID_AA64MMFR4_EL1.E2H0 < 0. HCR_EL2.E2H can be
* RES1 in that case. Publish the E2H bit early so that
* it can be picked up by the init_el2_state macro.
*
* Fruity CPUs seem to have HCR_EL2.E2H set to RAO/WI, but
* don't advertise it (they predate this relaxation).
*/
mrs_s x1, SYS_ID_AA64MMFR4_EL1
tbz x1, #(ID_AA64MMFR4_EL1_E2H0_SHIFT + ID_AA64MMFR4_EL1_E2H0_WIDTH - 1), 1f
orr x0, x0, #HCR_E2H
1:
msr hcr_el2, x0
isb
init_el2_hcr HCR_HOST_NVHE_FLAGS
init_el2_state
/* Hypervisor stub */

8
arch/arm64/kvm/hyp/nvhe/hyp-init.S
View File

@ -73,8 +73,12 @@ __do_hyp_init:
eret
SYM_CODE_END(__kvm_hyp_init)
/*
* Initialize EL2 CPU state to sane values.
*
* HCR_EL2.E2H must have been initialized already.
*/
SYM_CODE_START_LOCAL(__kvm_init_el2_state)
/* Initialize EL2 CPU state to sane values. */
init_el2_state // Clobbers x0..x2
finalise_el2_state
ret
@ -206,6 +210,8 @@ SYM_CODE_START_LOCAL(__kvm_hyp_init_cpu)
2: msr SPsel, #1 // We want to use SP_EL{1,2}
init_el2_hcr 0
bl __kvm_init_el2_state
__init_el2_nvhe_prepare_eret