Re: [PATCH 4/4] KVM: arm64: Add SMC hook for SME dvmsync erratum

[Will Deacon <will@kernel.org>]

On Mon, Mar 02, 2026 at 04:57:57PM +0000, Catalin Marinas wrote:
> 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
> affecteed CPUs. The implication is pages cannot be unmapped from the
> host stage2 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
> IPI 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.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Oliver Upton <oupton@kernel.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
> Cc: Sudeep Holla <sudeep.holla@kernel.org>
> ---
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c | 17 +++++++++++++++++
>  include/linux/arm-smccc.h             |  5 +++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 38f66a56a766..ab7f9273fddf 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>
> @@ -28,6 +30,15 @@ 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 (cpus_have_final_cap(ARM64_WORKAROUND_SME_DVMSYNC)) {
> +		struct arm_smccc_res res;
> +
> +		arm_smccc_1_1_smc(ARM_SMCCC_CPU_SME_DVMSYNC_WORKAROUND, &res);
> +	}
> +}
> +
>  static void guest_lock_component(struct pkvm_hyp_vm *vm)
>  {
>  	hyp_spin_lock(&vm->lock);
> @@ -553,6 +564,12 @@ int host_stage2_set_owner_locked(phys_addr_t addr, u64 size, u8 owner_id)
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * After stage2 maintenance has happened, but before the page owner has
> +	 * changed.
> +	 */
> +	pkvm_sme_dvmsync_fw_call();

Please note that this will conflict with my patch series adding support
for protected memory with pkvm. I _think_ the right answer is to
move this call into host_stage2_set_owner_metadata_locked().

Will