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BACKPORT: KVM: arm64: Implement PSCI SYSTEM_SUSPEND

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ARM DEN0022D.b 5.19 "SYSTEM_SUSPEND" describes a PSCI call that allows
software to request that a system be placed in the deepest possible
low-power state. Effectively, software can use this to suspend itself to
RAM.

Unfortunately, there really is no good way to implement a system-wide
PSCI call in KVM. Any precondition checks done in the kernel will need
to be repeated by userspace since there is no good way to protect a
critical section that spans an exit to userspace. SYSTEM_RESET and
SYSTEM_OFF are equally plagued by this issue, although no users have
seemingly cared for the relatively long time these calls have been
supported.

The solution is to just make the whole implementation userspace's
problem. Introduce a new system event, KVM_SYSTEM_EVENT_SUSPEND, that
indicates to userspace a calling vCPU has invoked PSCI SYSTEM_SUSPEND.
Additionally, add a CAP to get buy-in from userspace for this new exit
type.

Only advertise the SYSTEM_SUSPEND PSCI call if userspace has opted in.
If a vCPU calls SYSTEM_SUSPEND, punt straight to userspace. Provide
explicit documentation of userspace's responsibilites for the exit and
point to the PSCI specification to describe the actual PSCI call.

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220504032446.4133305-8-oupton@google.com
(cherry picked from commit bfbab44568)
[willdeacon@: Fixed conflicts in api.rst and uapi header due to missing KVM_CAP_*]
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Bug: 233588291
Change-Id: I3b9c5633ca1a65aa1c144db1c1bbc34aebfb0b15
This commit is contained in:
Oliver Upton
2022-05-04 03:24:41 +00:00
committed by Will Deacon
parent df1a2d7289
commit 4ddee168f4
5 changed files with 90 additions and 0 deletions
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15
include/uapi/linux/kvm.h
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@@ -434,6 +434,7 @@ struct kvm_run {
#define KVM_SYSTEM_EVENT_RESET 2
#define KVM_SYSTEM_EVENT_CRASH 3
#define KVM_SYSTEM_EVENT_WAKEUP 4
#define KVM_SYSTEM_EVENT_SUSPEND 5
__u32 type;
__u64 flags;
} system_event;
@@ -1114,6 +1115,20 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_BINARY_STATS_FD 203
#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
#define KVM_CAP_ARM_MTE 205
#if 0
/* Defined upstream but not backported to this kernel. */
#define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
#define KVM_CAP_VM_GPA_BITS 207
#define KVM_CAP_XSAVE2 208
#define KVM_CAP_SYS_ATTRIBUTES 209
#define KVM_CAP_PPC_AIL_MODE_3 210
#define KVM_CAP_S390_MEM_OP_EXTENSION 211
#define KVM_CAP_PMU_CAPABILITY 212
#define KVM_CAP_DISABLE_QUIRKS2 213
/* #define KVM_CAP_VM_TSC_CONTROL 214 */
#define KVM_CAP_SYSTEM_EVENT_DATA 215
#endif
#define KVM_CAP_ARM_SYSTEM_SUSPEND 216
#ifdef KVM_CAP_IRQ_ROUTING