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Message-ID: <CAJZ5v0jDzZDhorU+zE+dh+wd0cim9n2XQYZbMUDhyQ=DgDhNYw@mail.gmail.com>
Date: Thu, 29 Aug 2024 13:28:04 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Clément Léger <cleger@...osinc.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
	Robert Moore <robert.moore@...el.com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, acpica-devel@...ts.linux.dev
Subject: Re: [PATCH v2] ACPI: CPPC: Fix MASK_VAL() usage

On Mon, Aug 26, 2024 at 12:32 PM Clément Léger <cleger@...osinc.com> wrote:
>
> MASK_VAL() was added as a way to handle bit_offset and bit_width for
> registers located in system memory address space. However, while suited
> for reading, it does not work for writing and result in corrupted
> registers when writing values with bit_offset > 0. Moreover, when a
> register is collocated with another one at the same address but with a
> different mask, the current code results in the other registers being
> overwritten with 0s. The write procedure for SYSTEM_MEMORY registers
> should actually read the value, mask it, update it and write it with the
> updated value. Moreover, since registers can be located in the same
> word, we must take care of locking the access before doing it. We should
> potentially use a global lock since we don't know in if register
> addresses aren't shared with another _CPC package but better not
> encourage vendors to do so. Assume that registers can use the same word
> inside a _CPC package and thus, use a per _CPC package lock.
>
> Fixes: 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for system memory accesses")
> Signed-off-by: Clément Léger <cleger@...osinc.com>
>
> ---
> v2:
>  - Remove label and unlock the spinlock earlier.
>
>  drivers/acpi/cppc_acpi.c | 43 ++++++++++++++++++++++++++++++++++++----
>  include/acpi/cppc_acpi.h |  2 ++
>  2 files changed, 41 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 1d857978f5f4..4a47e08704d9 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -170,8 +170,11 @@ show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, wraparound_time);
>  #define GET_BIT_WIDTH(reg) ((reg)->access_width ? (8 << ((reg)->access_width - 1)) : (reg)->bit_width)
>
>  /* Shift and apply the mask for CPC reads/writes */
> -#define MASK_VAL(reg, val) (((val) >> (reg)->bit_offset) &                     \
> +#define MASK_VAL_READ(reg, val) (((val) >> (reg)->bit_offset) &                                \
>                                         GENMASK(((reg)->bit_width) - 1, 0))
> +#define MASK_VAL_WRITE(reg, prev_val, val)                                             \
> +       ((((val) & GENMASK(((reg)->bit_width) - 1, 0)) << (reg)->bit_offset) |          \
> +       ((prev_val) & ~(GENMASK(((reg)->bit_width) - 1, 0) << (reg)->bit_offset)))      \
>
>  static ssize_t show_feedback_ctrs(struct kobject *kobj,
>                 struct kobj_attribute *attr, char *buf)
> @@ -857,6 +860,7 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
>
>         /* Store CPU Logical ID */
>         cpc_ptr->cpu_id = pr->id;
> +       spin_lock_init(&cpc_ptr->rmw_lock);
>
>         /* Parse PSD data for this CPU */
>         ret = acpi_get_psd(cpc_ptr, handle);
> @@ -1062,7 +1066,7 @@ static int cpc_read(int cpu, struct cpc_register_resource *reg_res, u64 *val)
>         }
>
>         if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
> -               *val = MASK_VAL(reg, *val);
> +               *val = MASK_VAL_READ(reg, *val);
>
>         return 0;
>  }
> @@ -1071,9 +1075,11 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>  {
>         int ret_val = 0;
>         int size;
> +       u64 prev_val;
>         void __iomem *vaddr = NULL;
>         int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
>         struct cpc_reg *reg = &reg_res->cpc_entry.reg;
> +       struct cpc_desc *cpc_desc;
>
>         size = GET_BIT_WIDTH(reg);
>
> @@ -1106,8 +1112,34 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>                 return acpi_os_write_memory((acpi_physical_address)reg->address,
>                                 val, size);
>
> -       if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
> -               val = MASK_VAL(reg, val);
> +       if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
> +               cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> +               if (!cpc_desc) {
> +                       pr_debug("No CPC descriptor for CPU:%d\n", cpu);
> +                       return -ENODEV;
> +               }
> +
> +               spin_lock(&cpc_desc->rmw_lock);
> +               switch (size) {
> +               case 8:
> +                       prev_val = readb_relaxed(vaddr);
> +                       break;
> +               case 16:
> +                       prev_val = readw_relaxed(vaddr);
> +                       break;
> +               case 32:
> +                       prev_val = readl_relaxed(vaddr);
> +                       break;
> +               case 64:
> +                       prev_val = readq_relaxed(vaddr);
> +                       break;
> +               default:
> +                       spin_unlock(&cpc_desc->rmw_lock);
> +                       return -EFAULT;
> +               };
> +               val = MASK_VAL_WRITE(reg, prev_val, val);
> +               val |= prev_val;
> +       }
>
>         switch (size) {
>         case 8:
> @@ -1134,6 +1166,9 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>                 break;
>         }
>
> +       if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
> +               spin_unlock(&cpc_desc->rmw_lock);
> +
>         return ret_val;
>  }
>
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index 930b6afba6f4..e1720d930666 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -64,6 +64,8 @@ struct cpc_desc {
>         int cpu_id;
>         int write_cmd_status;
>         int write_cmd_id;
> +       /* Lock used for RMW operations in cpc_write() */
> +       spinlock_t rmw_lock;
>         struct cpc_register_resource cpc_regs[MAX_CPC_REG_ENT];
>         struct acpi_psd_package domain_info;
>         struct kobject kobj;
> --

Applied as 6.12 material, thanks!

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