[PATCH] KVM: arm64: Work around C1-Pro erratum 4193714 for protected guests

[PATCH] KVM: arm64: Work around C1-Pro erratum 4193714 for protected guests

[Catalin Marinas]

From: James Morse <james.morse@arm.com>

C1-Pro cores with SME have an erratum where TLBI+DSB does not complete
all outstanding SME accesses. Instead a DSB needs to be executed on the
affected CPUs. The implication is pages cannot be unmapped from the
host Stage 2 then provided to the guest. Host SME accesses may occur
after this point.

This erratum breaks pKVM's guarantees, and the workaround is hard to
implement as EL2 and EL1 share a security state meaning EL1 can mask
IPIs sent by EL2, leading to interrupt blackouts.

Instead, do this in EL3. This has the advantage of a separate security
state, meaning lower EL cannot mask the IPI. It is also simpler for EL3
to know about CPUs that are off or in PSCI's CPU_SUSPEND.

Add the needed hook to host_stage2_set_owner_metadata_locked(). This
covers the cases where the host loses access to a page:

  __pkvm_host_donate_guest()
  __pkvm_guest_unshare_host()
  host_stage2_set_owner_locked() when owner_id == PKVM_ID_HYP

Signed-off-by: James Morse <james.morse@arm.com>
[catalin.marinas@arm.com: move the hook to host_stage2_set_owner_metadata_locked()]
[catalin.marinas@arm.com: use hyp_smccc_1_1_smc()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Sudeep Holla <sudeep.holla@kernel.org>
---

That's a rebase to 7.1-rc1 together with a few tweaks. The initial
workaround for pKVM was posted here:

https://lore.kernel.org/r/20260323162408.4163113-6-catalin.marinas@arm.com

I dropped the vN numbering since the original series evolved a bit. I
also changed the subject here, more suitable for a stand-alone patch.

Changes since last time:

- Use hyp_smccc_1_1_smc() instead of arm_smccc_1_1_smc() as suggested by
  Vincent

- Do the SMC only when the host loses access to a page and not when the
  ownership transition happens in the other direction. Guests do not
  have access to SME in current mainline

I looked at the Android16 backport from Vincent and it covers more
cases but they do not apply to mainline (sglists, donate to FF-A). I
could not figure out why changing a host permission from RW to R or
!valid matters for this workaround, so that's not done here either.

 arch/arm64/kvm/hyp/nvhe/mem_protect.c | 20 +++++++++++++++++++-
 include/linux/arm-smccc.h             |  6 ++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 28a471d1927c..75977179c9d1 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -5,6 +5,8 @@
  */
 
 #include <linux/kvm_host.h>
+#include <linux/arm-smccc.h>
+
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_hyp.h>
 #include <asm/kvm_mmu.h>
@@ -14,6 +16,7 @@
 
 #include <hyp/fault.h>
 
+#include <nvhe/arm-smccc.h>
 #include <nvhe/gfp.h>
 #include <nvhe/memory.h>
 #include <nvhe/mem_protect.h>
@@ -29,6 +32,15 @@ static struct hyp_pool host_s2_pool;
 static DEFINE_PER_CPU(struct pkvm_hyp_vm *, __current_vm);
 #define current_vm (*this_cpu_ptr(&__current_vm))
 
+static void pkvm_sme_dvmsync_fw_call(void)
+{
+	if (alternative_has_cap_unlikely(ARM64_WORKAROUND_4193714)) {
+		struct arm_smccc_res res;
+
+		hyp_smccc_1_1_smc(ARM_SMCCC_CPU_WORKAROUND_4193714, &res);
+	}
+}
+
 static void guest_lock_component(struct pkvm_hyp_vm *vm)
 {
 	hyp_spin_lock(&vm->lock);
@@ -574,8 +586,14 @@ static int host_stage2_set_owner_metadata_locked(phys_addr_t addr, u64 size,
 	ret = host_stage2_try(kvm_pgtable_stage2_annotate, &host_mmu.pgt,
 			      addr, size, &host_s2_pool,
 			      KVM_HOST_INVALID_PTE_TYPE_DONATION, annotation);
-	if (!ret)
+	if (!ret) {
+		/*
+		 * After stage2 maintenance has happened, but before the page
+		 * owner has changed.
+		 */
+		pkvm_sme_dvmsync_fw_call();
 		__host_update_page_state(addr, size, PKVM_NOPAGE);
+	}
 
 	return ret;
 }
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 50b47eba7d01..e7195750d21b 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -105,6 +105,12 @@
 			   ARM_SMCCC_SMC_32,				\
 			   0, 0x3fff)
 
+/* C1-Pro erratum 4193714: SME DVMSync early acknowledgement */
+#define ARM_SMCCC_CPU_WORKAROUND_4193714				\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_CPU, 0x10)
+
 #define ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID				\
 	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
 			   ARM_SMCCC_SMC_32,				\