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From:   Fabiano Rosas <farosas@linux.ibm.com>
To:     "Pratik R. Sampat" <psampat@linux.ibm.com>, mpe@ellerman.id.au,
        benh@kernel.crashing.org, paulus@samba.org,
        linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org,
        linux-kernel@vger.kernel.org, psampat@linux.ibm.com,
        pratik.r.sampat@gmail.com
Subject: Re: [PATCH v3 1/1] powerpc/pseries: Interface to represent PAPR
 firmware attributes
In-Reply-To: <20210712105140.33388-2-psampat@linux.ibm.com>
References: <20210712105140.33388-1-psampat@linux.ibm.com>
 <20210712105140.33388-2-psampat@linux.ibm.com>
Date:   Mon, 12 Jul 2021 12:43:47 -0300
Message-ID: <87lf6bo7v0.fsf@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

"Pratik R. Sampat" <psampat@linux.ibm.com> writes:

Hi, have you seen Documentation/core-api/kobject.rst, particularly the
part that says:

"When you see a sysfs directory full of other directories, generally each
   of those directories corresponds to a kobject in the same kset."

Taking a look at samples/kobject/kset-example.c, it seems to provide an
overall structure that is closer to what other modules do when creating
sysfs entries. It uses less dynamic allocations and deals a bit better
with cleaning up the state afterwards.

> Adds a generic interface to represent the energy and frequency related
> PAPR attributes on the system using the new H_CALL
> "H_GET_ENERGY_SCALE_INFO".
>
> H_GET_EM_PARMS H_CALL was previously responsible for exporting this
> information in the lparcfg, however the H_GET_EM_PARMS H_CALL
> will be deprecated P10 onwards.
>
> The H_GET_ENERGY_SCALE_INFO H_CALL is of the following call format:
> hcall(
>   uint64 H_GET_ENERGY_SCALE_INFO,  // Get energy scale info
>   uint64 flags,           // Per the flag request
>   uint64 firstAttributeId,// The attribute id
>   uint64 bufferAddress,   // Guest physical address of the output buffer
>   uint64 bufferSize       // The size in bytes of the output buffer
> );
>
> This H_CALL can query either all the attributes at once with
> firstAttributeId = 0, flags = 0 as well as query only one attribute
> at a time with firstAttributeId = id, flags = 1.
>
> The output buffer consists of the following
> 1. number of attributes              - 8 bytes
> 2. array offset to the data location - 8 bytes
> 3. version info                      - 1 byte
> 4. A data array of size num attributes, which contains the following:
>   a. attribute ID              - 8 bytes
>   b. attribute value in number - 8 bytes
>   c. attribute name in string  - 64 bytes
>   d. attribute value in string - 64 bytes
>
> The new H_CALL exports information in direct string value format, hence
> a new interface has been introduced in
> /sys/firmware/papr/energy_scale_info to export this information to
> userspace in an extensible pass-through format.
>
> The H_CALL returns the name, numeric value and string value (if exists)
>
> The format of exposing the sysfs information is as follows:
> /sys/firmware/papr/energy_scale_info/
>    |-- <id>/
>      |-- desc
>      |-- value
>      |-- value_desc (if exists)
>    |-- <id>/
>      |-- desc
>      |-- value
>      |-- value_desc (if exists)
> ...
>
> The energy information that is exported is useful for userspace tools
> such as powerpc-utils. Currently these tools infer the
> "power_mode_data" value in the lparcfg, which in turn is obtained from
> the to be deprecated H_GET_EM_PARMS H_CALL.
> On future platforms, such userspace utilities will have to look at the
> data returned from the new H_CALL being populated in this new sysfs
> interface and report this information directly without the need of
> interpretation.
>
> Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>
> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> ---
>  .../sysfs-firmware-papr-energy-scale-info     |  26 ++
>  arch/powerpc/include/asm/hvcall.h             |  24 +-
>  arch/powerpc/kvm/trace_hv.h                   |   1 +
>  arch/powerpc/platforms/pseries/Makefile       |   3 +-
>  .../pseries/papr_platform_attributes.c        | 320 ++++++++++++++++++
>  5 files changed, 372 insertions(+), 2 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-firmware-papr-energy-scale-info
>  create mode 100644 arch/powerpc/platforms/pseries/papr_platform_attributes.c
>
> diff --git a/Documentation/ABI/testing/sysfs-firmware-papr-energy-scale-info b/Documentation/ABI/testing/sysfs-firmware-papr-energy-scale-info
> new file mode 100644
> index 000000000000..fd82f2bfafe5
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-papr-energy-scale-info
> @@ -0,0 +1,26 @@
> +What:		/sys/firmware/papr/energy_scale_info
> +Date:		June 2021
> +Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
> +Description:	Directory hosting a set of platform attributes like
> +		energy/frequency on Linux running as a PAPR guest.
> +
> +		Each file in a directory contains a platform
> +		attribute hierarchy pertaining to performance/
> +		energy-savings mode and processor frequency.
> +
> +What:		/sys/firmware/papr/energy_scale_info/<id>
> +		/sys/firmware/papr/energy_scale_info/<id>/desc
> +		/sys/firmware/papr/energy_scale_info/<id>/value
> +		/sys/firmware/papr/energy_scale_info/<id>/value_desc
> +Date:		June 2021
> +Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
> +Description:	Energy, frequency attributes directory for POWERVM servers
> +
> +		This directory provides energy, erequency, folding information. It

s/erequency/frequency/

> +		contains below sysfs attributes:
> +
> +		- desc: String description of the attribute <id>
> +
> +		- value: Numeric value of attribute <id>
> +
> +		- value_desc: String value of attribute <id>
> diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
> index e3b29eda8074..c91714ea6719 100644
> --- a/arch/powerpc/include/asm/hvcall.h
> +++ b/arch/powerpc/include/asm/hvcall.h
> @@ -316,7 +316,8 @@
>  #define H_SCM_PERFORMANCE_STATS 0x418
>  #define H_RPT_INVALIDATE	0x448
>  #define H_SCM_FLUSH		0x44C
> -#define MAX_HCALL_OPCODE	H_SCM_FLUSH
> +#define H_GET_ENERGY_SCALE_INFO	0x450
> +#define MAX_HCALL_OPCODE	H_GET_ENERGY_SCALE_INFO
>
>  /* Scope args for H_SCM_UNBIND_ALL */
>  #define H_UNBIND_SCOPE_ALL (0x1)
> @@ -631,6 +632,27 @@ struct hv_gpci_request_buffer {
>  	uint8_t bytes[HGPCI_MAX_DATA_BYTES];
>  } __packed;
>
> +#define ESI_VERSION	0x1
> +#define MAX_ESI_ATTRS	10
> +#define MAX_BUF_SZ	(sizeof(struct h_energy_scale_info_hdr) + \
> +			(sizeof(struct energy_scale_attribute) * MAX_ESI_ATTRS))
> +
> +struct energy_scale_attribute {
> +	__be64 id;
> +	__be64 value;
> +	unsigned char desc[64];
> +	unsigned char value_desc[64];
> +} __packed;
> +
> +struct h_energy_scale_info_hdr {
> +	__be64 num_attrs;
> +	__be64 array_offset;
> +	__u8 data_header_version;
> +} __packed;
> +
> +/* /sys/firmware/papr */
> +extern struct kobject *papr_kobj;
> +
>  #endif /* __ASSEMBLY__ */
>  #endif /* __KERNEL__ */
>  #endif /* _ASM_POWERPC_HVCALL_H */
> diff --git a/arch/powerpc/kvm/trace_hv.h b/arch/powerpc/kvm/trace_hv.h
> index 830a126e095d..38cd0ed0a617 100644
> --- a/arch/powerpc/kvm/trace_hv.h
> +++ b/arch/powerpc/kvm/trace_hv.h
> @@ -115,6 +115,7 @@
>  	{H_VASI_STATE,			"H_VASI_STATE"}, \
>  	{H_ENABLE_CRQ,			"H_ENABLE_CRQ"}, \
>  	{H_GET_EM_PARMS,		"H_GET_EM_PARMS"}, \
> +	{H_GET_ENERGY_SCALE_INFO,	"H_GET_ENERGY_SCALE_INFO"}, \
>  	{H_SET_MPP,			"H_SET_MPP"}, \
>  	{H_GET_MPP,			"H_GET_MPP"}, \
>  	{H_HOME_NODE_ASSOCIATIVITY,	"H_HOME_NODE_ASSOCIATIVITY"}, \
> diff --git a/arch/powerpc/platforms/pseries/Makefile b/arch/powerpc/platforms/pseries/Makefile
> index c8a2b0b05ac0..d14fca89ac25 100644
> --- a/arch/powerpc/platforms/pseries/Makefile
> +++ b/arch/powerpc/platforms/pseries/Makefile
> @@ -6,7 +6,8 @@ obj-y			:= lpar.o hvCall.o nvram.o reconfig.o \
>  			   of_helpers.o \
>  			   setup.o iommu.o event_sources.o ras.o \
>  			   firmware.o power.o dlpar.o mobility.o rng.o \
> -			   pci.o pci_dlpar.o eeh_pseries.o msi.o
> +			   pci.o pci_dlpar.o eeh_pseries.o msi.o \
> +			   papr_platform_attributes.o
>  obj-$(CONFIG_SMP)	+= smp.o
>  obj-$(CONFIG_SCANLOG)	+= scanlog.o
>  obj-$(CONFIG_KEXEC_CORE)	+= kexec.o
> diff --git a/arch/powerpc/platforms/pseries/papr_platform_attributes.c b/arch/powerpc/platforms/pseries/papr_platform_attributes.c
> new file mode 100644
> index 000000000000..43c620132b4d
> --- /dev/null
> +++ b/arch/powerpc/platforms/pseries/papr_platform_attributes.c
> @@ -0,0 +1,320 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Platform energy and frequency attributes driver
> + *
> + * This driver creates a sys file at /sys/firmware/papr/ which encapsulates a
> + * directory structure containing files in keyword - value pairs that specify
> + * energy and frequency configuration of the system.
> + *
> + * The format of exposing the sysfs information is as follows:
> + * /sys/firmware/papr/energy_scale_info/
> + *  |-- <id>/
> + *    |-- desc
> + *    |-- value
> + *    |-- value_desc (if exists)
> + *  |-- <id>/
> + *    |-- desc
> + *    |-- value
> + *    |-- value_desc (if exists)
> + *
> + * Copyright 2021 IBM Corp.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/errno.h>
> +#include <linux/init.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/hugetlb.h>
> +#include <asm/lppaca.h>
> +#include <asm/hvcall.h>
> +#include <asm/firmware.h>
> +#include <asm/time.h>
> +#include <asm/prom.h>
> +#include <asm/vdso_datapage.h>
> +#include <asm/vio.h>
> +#include <asm/mmu.h>
> +#include <asm/machdep.h>
> +#include <asm/drmem.h>
> +
> +#include "pseries.h"
> +
> +#define MAX_ATTRS		3
> +#define MAX_NAME_LEN		16
> +
> +/*
> + * Flag attributes to fetch either all or one attribute from the HCALL
> + * flag = BE(0) => fetch all attributes with firstAttributeId = 0
> + * flag = BE(1) => fetch a single attribute with firstAttributeId = id
> + */
> +#define ESI_FLAGS_ALL		0
> +#define ESI_FLAGS_SINGLE	PPC_BIT(0)
> +
> +struct papr_attr {
> +	u64 id;
> +	struct kobj_attribute kobj_attr;
> +};
> +struct papr_group {
> +	char name[MAX_NAME_LEN];

This is unused.

> +	struct attribute_group pg;
> +	struct papr_attr *pgattrs;

This is always MAX_ATTRS long, we could define it statically and avoid a
kmalloc later.

> +} *pgs;
> +
> +/* /sys/firmware/papr */
> +struct kobject *papr_kobj;
> +/* /sys/firmware/papr/energy_scale_info */
> +struct kobject *esi_kobj;
> +
> +struct h_energy_scale_info_hdr *esi_hdr;
> +struct energy_scale_attribute *esi_attrs;
> +
> +/*
> + * Extract and export the description of the energy scale attribute
> + *
> + * As We do not expect the name to change, hence use the old description and
> + * save a call to the H_GET_ENERGY_SCALE_INFO HCALL
> + */
> +static ssize_t papr_show_desc(struct kobject *kobj,
> +			       struct kobj_attribute *kobj_attr,
> +			       char *buf)
> +{
> +	struct papr_attr *pattr = container_of(kobj_attr, struct papr_attr,
> +					       kobj_attr);
> +	int idx, ret = 0;
> +
> +	for (idx = 0; idx < be64_to_cpu(esi_hdr->num_attrs); idx++) {
> +		if (pattr->id == be64_to_cpu(esi_attrs[idx].id)) {
> +			ret = sprintf(buf, "%s\n", esi_attrs[idx].desc);

We know the size of desc, so could use snprintf here.

> +			if (ret < 0)
> +				ret = -EIO;
> +			break;
> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +/*
> + * Extract and export the numeric value of the energy scale attributes
> + */
> +static ssize_t papr_show_value(struct kobject *kobj,
> +				struct kobj_attribute *kobj_attr,
> +				char *buf)
> +{
> +	struct papr_attr *pattr = container_of(kobj_attr, struct papr_attr,
> +					       kobj_attr);
> +	char *t_buf;
> +	struct h_energy_scale_info_hdr *t_hdr;
> +	struct energy_scale_attribute *t_esi;
> +	int ret = 0;
> +
> +	t_buf = kmalloc(MAX_BUF_SZ, GFP_KERNEL);
> +	if (t_buf == NULL)
> +		return -ENOMEM;
> +
> +	ret = plpar_hcall_norets(H_GET_ENERGY_SCALE_INFO, ESI_FLAGS_SINGLE,
> +				 pattr->id, virt_to_phys(t_buf),
> +				 MAX_BUF_SZ);
> +
> +	if (ret != H_SUCCESS) {
> +		pr_warn("hcall failed: H_GET_ENERGY_SCALE_INFO");
> +		goto out;
> +	}
> +
> +	t_hdr = (struct h_energy_scale_info_hdr *) t_buf;
> +	t_esi = (struct energy_scale_attribute *)
> +		(t_buf + be64_to_cpu(t_hdr->array_offset));
> +
> +	ret = sprintf(buf, "%llu\n", be64_to_cpu(t_esi->value));

snprintf

> +	if (ret < 0)
> +		ret = -EIO;
> +out:
> +	kfree(t_buf);
> +
> +	return ret;
> +}
> +
> +/*
> + * Extract and export the value description in string format of the energy
> + * scale attributes
> + */
> +static ssize_t papr_show_value_desc(struct kobject *kobj,
> +				     struct kobj_attribute *kobj_attr,
> +				     char *buf)
> +{
> +	struct papr_attr *pattr = container_of(kobj_attr, struct papr_attr,
> +					       kobj_attr);
> +	char *t_buf;
> +	struct h_energy_scale_info_hdr *t_hdr;
> +	struct energy_scale_attribute *t_esi;
> +	int ret = 0;
> +
> +	t_buf = kmalloc(MAX_BUF_SZ, GFP_KERNEL);
> +	if (t_buf == NULL)
> +		return -ENOMEM;
> +
> +	ret = plpar_hcall_norets(H_GET_ENERGY_SCALE_INFO, ESI_FLAGS_SINGLE,
> +				 pattr->id, virt_to_phys(t_buf),
> +				 MAX_BUF_SZ);
> +
> +	if (ret != H_SUCCESS) {
> +		pr_warn("hcall failed: H_GET_ENERGY_SCALE_INFO");
> +		goto out;
> +	}
> +
> +	t_hdr = (struct h_energy_scale_info_hdr *) t_buf;
> +	t_esi = (struct energy_scale_attribute *)
> +		(t_buf + be64_to_cpu(t_hdr->array_offset));
> +
> +	ret = sprintf(buf, "%s\n", t_esi->value_desc);

snprintf

> +	if (ret < 0)
> +		ret = -EIO;
> +out:
> +	kfree(t_buf);
> +
> +	return ret;
> +}
> +
> +static struct papr_ops_info {
> +	const char *attr_name;
> +	ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *kobj_attr,
> +			char *buf);
> +} ops_info[MAX_ATTRS] = {
> +	{ "desc", papr_show_desc },
> +	{ "value", papr_show_value },
> +	{ "value_desc", papr_show_value_desc },
> +};
> +
> +static void add_attr(u64 id, int index, struct papr_attr *attr)
> +{
> +	attr->id = id;
> +	sysfs_attr_init(&attr->kobj_attr.attr);
> +	attr->kobj_attr.attr.name = ops_info[index].attr_name;
> +	attr->kobj_attr.attr.mode = 0444;
> +	attr->kobj_attr.show = ops_info[index].show;
> +}
> +
> +static int add_attr_group(u64 id, int len, struct papr_group *pg,
> +			  bool show_val_desc)
> +{
> +	int i;
> +
> +	for (i = 0; i < len; i++) {
> +		if (!strcmp(ops_info[i].attr_name, "value_desc") &&
> +		    !show_val_desc) {
> +			continue;
> +		}
> +		add_attr(id, i, &pg->pgattrs[i]);
> +		pg->pg.attrs[i] = &pg->pgattrs[i].kobj_attr.attr;
> +	}
> +
> +	return sysfs_create_group(esi_kobj, &pg->pg);
> +}
> +
> +static int __init papr_init(void)
> +{
> +	uint64_t num_attrs;
> +	int ret, idx, i;
> +	char *esi_buf;
> +
> +	if (!firmware_has_feature(FW_FEATURE_LPAR))
> +		return -ENXIO;
> +
> +	esi_buf = kmalloc(MAX_BUF_SZ, GFP_KERNEL);

This memory is never released. I don't think it's worth it just to save
a hcall.

> +	if (esi_buf == NULL)
> +		return -ENOMEM;
> +	/*
> +	 * hcall(
> +	 * uint64 H_GET_ENERGY_SCALE_INFO,  // Get energy scale info
> +	 * uint64 flags,            // Per the flag request
> +	 * uint64 firstAttributeId, // The attribute id
> +	 * uint64 bufferAddress,    // Guest physical address of the output buffer
> +	 * uint64 bufferSize);      // The size in bytes of the output buffer
> +	 */
> +	ret = plpar_hcall_norets(H_GET_ENERGY_SCALE_INFO, ESI_FLAGS_ALL, 0,
> +				 virt_to_phys(esi_buf), MAX_BUF_SZ);
> +	esi_hdr = (struct h_energy_scale_info_hdr *) esi_buf;
> +	if (ret != H_SUCCESS || esi_hdr->data_header_version != ESI_VERSION) {

I really dislike this. If you want to bail due to version change, then
at least include in the ABI document that we might not give the
userspace any data at all.

> +		pr_warn("hcall failed: H_GET_ENERGY_SCALE_INFO");
> +		goto out;
> +	}
> +
> +	num_attrs = be64_to_cpu(esi_hdr->num_attrs);
> +	/*
> +	 * Typecast the energy buffer to the attribute structure at the offset
> +	 * specified in the buffer
> +	 */

I think the code is now simple enough that this comment could be
removed.

> +	esi_attrs = (struct energy_scale_attribute *)
> +		    (esi_buf + be64_to_cpu(esi_hdr->array_offset));
> +
> +	pgs = kcalloc(num_attrs, sizeof(*pgs), GFP_KERNEL);

This is never freed.

> +	if (!pgs)
> +		goto out_pgs;
> +
> +	papr_kobj = kobject_create_and_add("papr", firmware_kobj);
> +	if (!papr_kobj) {
> +		pr_warn("kobject_create_and_add papr failed\n");
> +		goto out_kobj;
> +	}
> +
> +	esi_kobj = kobject_create_and_add("energy_scale_info", papr_kobj);
> +	if (!esi_kobj) {
> +		pr_warn("kobject_create_and_add energy_scale_info failed\n");
> +		goto out_ekobj;
> +	}
> +
> +	for (idx = 0; idx < num_attrs; idx++) {
> +		char buf[4];
> +		bool show_val_desc = true;
> +
> +		pgs[idx].pgattrs = kcalloc(MAX_ATTRS,
> +					   sizeof(*pgs[idx].pgattrs),
> +					   GFP_KERNEL);
> +		if (!pgs[idx].pgattrs)
> +			goto out_kobj;
> +
> +		pgs[idx].pg.attrs = kcalloc(MAX_ATTRS + 1,
> +					    sizeof(*pgs[idx].pg.attrs),
> +					    GFP_KERNEL);

I think the kobject code expects this to be statically allocated, so
you'd need to override the release function in some way to be able to
free this.

> +		if (!pgs[idx].pg.attrs) {
> +			kfree(pgs[idx].pgattrs);
> +			goto out_kobj;
> +		}
> +
> +		sprintf(buf, "%lld", be64_to_cpu(esi_attrs[idx].id));

Do you mean pgs[idx].name instead of buf? Otherwise you're passing this
stack allocated 'buf' to another function.

> +		pgs[idx].pg.name = buf;
> +
> +		/* Do not add the value description if it does not exist */
> +		if (strlen(esi_attrs[idx].value_desc) == 0)
> +			show_val_desc = false;
> +
> +		if (add_attr_group(be64_to_cpu(esi_attrs[idx].id),
> +				   MAX_ATTRS, &pgs[idx], show_val_desc)) {
> +			pr_warn("Failed to create papr attribute group %s\n",
> +				pgs[idx].pg.name);
> +			goto out_pgattrs;
> +		}
> +	}
> +
> +	return 0;
> +
> +out_pgattrs:
> +	for (i = 0; i < MAX_ATTRS; i++) {
> +		kfree(pgs[i].pgattrs);
> +		kfree(pgs[i].pg.attrs);
> +	}
> +out_ekobj:
> +	kobject_put(esi_kobj);
> +out_kobj:
> +	kobject_put(papr_kobj);
> +out_pgs:
> +	kfree(pgs);
> +out:
> +	kfree(esi_buf);
> +
> +	return -ENOMEM;
> +}
> +
> +machine_device_initcall(pseries, papr_init);