Re: [PATCH v4 7/7] platform/x86/amd/hsmp: Make metric table read locking use guard(mutex)

[Ilpo Järvinen]

On Thu, 28 May 2026, Muralidhara M K wrote:

> hsmp_metric_tbl_read() refreshes the SMU-side metric table and then
> memcpy_fromio()'s the result. Without serialization, two parallel
> readers can interleave the refresh and the copy and the caller
> observes a torn (mixed old/new) snapshot. Add a per-socket
> metric_tbl_lock so the refresh-and-copy sequence is atomic from
> userspace's point of view.
> 
> Use scoped guard(mutex) so the lock is released on every return
> path without hand-written goto chains, and initialize the mutex
> with devm_mutex_init() so no explicit mutex_destroy() cleanup is
> required.
> 
> Initialize the mutex before devm_ioremap() so the invariant
> "sock->metric_tbl_addr != NULL implies metric_tbl_lock is usable"
> holds on every error exit. Both callers of hsmp_get_tbl_dram_base()
> (init_acpi() and init_platform_device()) intentionally only log a
> failure and continue probing, so initializing the mutex after a
> successful ioremap would leave sock->metric_tbl_addr populated with
> an uninitialized lock, and the next hsmp_metric_tbl_read() would
> take guard(mutex)() on garbage memory. With the order swapped, a
> devm_mutex_init() failure returns early before metric_tbl_addr is
> ever set, and the existing NULL check in hsmp_metric_tbl_read()
> keeps rejecting the read with -ENOMEM as before.
> 
> Co-developed-by: Muthusamy Ramalingam <muthusamy.ramalingam@xxxxxxx>
> Signed-off-by: Muthusamy Ramalingam <muthusamy.ramalingam@xxxxxxx>
> Signed-off-by: Muralidhara M K <muralidhara.mk@xxxxxxx>
> ---
>  drivers/platform/x86/amd/hsmp/hsmp.c | 20 ++++++++++++++++++++
>  drivers/platform/x86/amd/hsmp/hsmp.h |  3 +++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/drivers/platform/x86/amd/hsmp/hsmp.c b/drivers/platform/x86/amd/hsmp/hsmp.c
> index 67f0074bb532..fda57225939c 100644
> --- a/drivers/platform/x86/amd/hsmp/hsmp.c
> +++ b/drivers/platform/x86/amd/hsmp/hsmp.c
> @@ -479,6 +479,7 @@ ssize_t hsmp_metric_tbl_read(struct hsmp_socket *sock, char *buf, size_t size)
>  	msg.msg_id	= HSMP_GET_METRIC_TABLE;
>  	msg.sock_ind	= sock->sock_ind;
>  
> +	guard(mutex)(&sock->metric_tbl_lock);
>  	ret = hsmp_send_message(&msg);
>  	if (ret)
>  		return ret;
> @@ -495,6 +496,24 @@ int hsmp_get_tbl_dram_base(u16 sock_ind)
>  	phys_addr_t dram_addr;
>  	int ret;
>  
> +	/*
> +	 * Initialize the per-socket lock before anything that can set
> +	 * sock->metric_tbl_addr to a non-NULL value.  hsmp_metric_tbl_read()
> +	 * gates on sock->metric_tbl_addr being non-NULL and then takes
> +	 * metric_tbl_lock unconditionally; both callers of this function
> +	 * (init_acpi() and init_platform_device()) intentionally only log
> +	 * a failure here and continue probing, so an init order that left
> +	 * metric_tbl_addr populated while devm_mutex_init() failed would
> +	 * leave the read path locking an uninitialized mutex.  Doing the
> +	 * mutex init first preserves the invariant "metric_tbl_addr !=
> +	 * NULL implies the lock is usable" on every error exit.
> +	 */
> +	ret = devm_mutex_init(sock->dev, &sock->metric_tbl_lock);
> +	if (ret) {
> +		dev_err(sock->dev, "Failed to initialize metric table lock\n");
> +		return ret;
> +	}
> +
>  	msg.sock_ind	= sock_ind;
>  	msg.response_sz	= hsmp_msg_desc_table[HSMP_GET_METRIC_TABLE_DRAM_ADDR].response_sz;
>  	msg.msg_id	= HSMP_GET_METRIC_TABLE_DRAM_ADDR;
> @@ -524,6 +543,7 @@ int hsmp_get_tbl_dram_base(u16 sock_ind)
>  		dev_err(sock->dev, "Failed to ioremap metric table addr\n");
>  		return -ENOMEM;
>  	}
> +
>  	return 0;

A spurious change.

>  }
>  EXPORT_SYMBOL_NS_GPL(hsmp_get_tbl_dram_base, "AMD_HSMP");
> diff --git a/drivers/platform/x86/amd/hsmp/hsmp.h b/drivers/platform/x86/amd/hsmp/hsmp.h
> index e7f051475728..f7b1cbf19932 100644
> --- a/drivers/platform/x86/amd/hsmp/hsmp.h
> +++ b/drivers/platform/x86/amd/hsmp/hsmp.h
> @@ -15,6 +15,7 @@
>  #include <linux/hwmon.h>
>  #include <linux/kconfig.h>
>  #include <linux/miscdevice.h>
> +#include <linux/mutex.h>
>  #include <linux/pci.h>
>  #include <linux/semaphore.h>
>  #include <linux/sysfs.h>
> @@ -41,6 +42,8 @@ struct hsmp_socket {
>  	struct bin_attribute hsmp_attr;
>  	struct hsmp_mbaddr_info mbinfo;
>  	void __iomem *metric_tbl_addr;
> +	/* Serializes concurrent metric table refreshes from the sysfs path */
> +	struct mutex metric_tbl_lock;
>  	void __iomem *virt_base_addr;
>  	struct semaphore hsmp_sem;
>  	char name[HSMP_ATTR_GRP_NAME_SIZE];
> 

-- 
 i.