Re: [PATCH v5 12/22] RISC-V: KVM: Implement SBI PMU Snapshot feature

[Andrew Jones <ajones@ventanamicro.com>]

On Wed, Apr 03, 2024 at 01:04:41AM -0700, Atish Patra wrote:
> PMU Snapshot function allows to minimize the number of traps when the
> guest access configures/access the hpmcounters. If the snapshot feature
> is enabled, the hypervisor updates the shared memory with counter
> data and state of overflown counters. The guest can just read the
> shared memory instead of trap & emulate done by the hypervisor.
> 
> This patch doesn't implement the counter overflow yet.
> 
> Reviewed-by: Anup Patel <anup@brainfault.org>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_pmu.h |   7 ++
>  arch/riscv/kvm/vcpu_pmu.c             | 121 +++++++++++++++++++++++++-
>  arch/riscv/kvm/vcpu_sbi_pmu.c         |   3 +
>  3 files changed, 130 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> index 395518a1664e..77a1fc4d203d 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_pmu.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> @@ -50,6 +50,10 @@ struct kvm_pmu {
>  	bool init_done;
>  	/* Bit map of all the virtual counter used */
>  	DECLARE_BITMAP(pmc_in_use, RISCV_KVM_MAX_COUNTERS);
> +	/* The address of the counter snapshot area (guest physical address) */
> +	gpa_t snapshot_addr;
> +	/* The actual data of the snapshot */
> +	struct riscv_pmu_snapshot_data *sdata;
>  };
>  
>  #define vcpu_to_pmu(vcpu) (&(vcpu)->arch.pmu_context)
> @@ -85,6 +89,9 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>  int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
>  				struct kvm_vcpu_sbi_return *retdata);
>  void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu);
> +int kvm_riscv_vcpu_pmu_snapshot_set_shmem(struct kvm_vcpu *vcpu, unsigned long saddr_low,
> +				      unsigned long saddr_high, unsigned long flags,
> +				      struct kvm_vcpu_sbi_return *retdata);
>  void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu);
>  void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
>  
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 2d9929bbc2c8..f706c688b338 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -14,6 +14,7 @@
>  #include <asm/csr.h>
>  #include <asm/kvm_vcpu_sbi.h>
>  #include <asm/kvm_vcpu_pmu.h>
> +#include <asm/sbi.h>
>  #include <linux/bitops.h>
>  
>  #define kvm_pmu_num_counters(pmu) ((pmu)->num_hw_ctrs + (pmu)->num_fw_ctrs)
> @@ -311,6 +312,80 @@ int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
>  	return ret;
>  }
>  
> +static void kvm_pmu_clear_snapshot_area(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +	int snapshot_area_size = sizeof(struct riscv_pmu_snapshot_data);
> +
> +	if (kvpmu->sdata) {
> +		if (kvpmu->snapshot_addr != INVALID_GPA) {
> +			memset(kvpmu->sdata, 0, snapshot_area_size);
> +			kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr,
> +					     kvpmu->sdata, snapshot_area_size);
> +		} else {
> +			pr_warn("snapshot address invalid\n");
> +		}
> +		kfree(kvpmu->sdata);
> +		kvpmu->sdata = NULL;
> +	}
> +	kvpmu->snapshot_addr = INVALID_GPA;
> +}
> +
> +int kvm_riscv_vcpu_pmu_snapshot_set_shmem(struct kvm_vcpu *vcpu, unsigned long saddr_low,
> +				      unsigned long saddr_high, unsigned long flags,
> +				      struct kvm_vcpu_sbi_return *retdata)
> +{
> +	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +	int snapshot_area_size = sizeof(struct riscv_pmu_snapshot_data);
> +	int sbiret = 0;
> +	gpa_t saddr;
> +	unsigned long hva;
> +	bool writable;
> +
> +	if (!kvpmu || flags) {
> +		sbiret = SBI_ERR_INVALID_PARAM;
> +		goto out;
> +	}
> +
> +	if (saddr_low == SBI_SHMEM_DISABLE && saddr_high == SBI_SHMEM_DISABLE) {
> +		kvm_pmu_clear_snapshot_area(vcpu);
> +		return 0;
> +	}
> +
> +	saddr = saddr_low;
> +
> +	if (saddr_high != 0) {
> +		if (IS_ENABLED(CONFIG_32BIT))
> +			saddr |= ((gpa_t)saddr << 32);

saddr |= ((gpa_t)saddr_high << 32)

> +		else
> +			sbiret = SBI_ERR_INVALID_ADDRESS;
> +		goto out;
> +	}
> +

Thanks,
drew

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