Re: [PATCH v3 7/7] platform/x86/amd/hsmp: Make metric table read locking use guard(mutex)

[M K, Muralidhara]

On 5/22/2026 4:25 PM, Ilpo Järvinen wrote:
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>
>
> On Sun, 17 May 2026, Muralidhara M K wrote:
>
> > Add a per-socket mutex (metric_tbl_lock) to serialize concurrent reads
> > on the metric table. Without serialization, two simultaneous
> > readers could interleave the SMU refresh command and the
> > memcpy_fromio(), producing a torn (mixed old/new) snapshot.
> >
> > Use scoped guard(mutex) in hsmp_metric_tbl_read() so the lock is
> > automatically released on all return paths. Initialize the mutex with
> > devm_mutex_init() in hsmp_get_tbl_dram_base() and return an error if
> > initialization fails, avoiding manual mutex_destroy() cleanup paths.
> >
> > 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>
> > ---
> > Changes:
> > v1->v2: Add lock
> > v2->v3: Replace mutex_init to devm_mutex_init call
> >
> >   drivers/platform/x86/amd/hsmp/hsmp.c | 8 ++++++++
> >   drivers/platform/x86/amd/hsmp/hsmp.h | 3 +++
> >   2 files changed, 11 insertions(+)
> >
> > diff --git a/drivers/platform/x86/amd/hsmp/hsmp.c b/drivers/platform/x86/amd/hsmp/hsmp.c
> > index 3a02d683dea0..2fec897a95be 100644
> > --- a/drivers/platform/x86/amd/hsmp/hsmp.c
> > +++ b/drivers/platform/x86/amd/hsmp/hsmp.c
> > @@ -447,6 +447,7 @@ 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;
> > @@ -492,6 +493,13 @@ int hsmp_get_tbl_dram_base(u16 sock_ind)
> >                dev_err(sock->dev, "Failed to ioremap metric table addr\n");
> >                return -ENOMEM;
> >        }
> > +
> > +     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;
> > +     }
>
> Sashiko notes a potential problem with this failing and that not resulting
> in a probe fail, which leaves the mutex uninitialized.
>
> But the mutex could be initialized earlier to avoid the problem I think.
In the v2 series, you suggested using devm_mutex_init(). However, I will 
test it and initialize it earlier if required.

> > +
> >        return 0;
> >   }
> >   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.