Re: [PATCH] soc: qcom: cmd-db: map shared memory as WT, not WB

[Elliot Berman]

On Thu, Mar 28, 2024 at 07:40:49PM -0500, Stephen Boyd wrote:
> Quoting Stephan Gerhold (2024-03-28 02:58:56)
> >
> > FWIW: This old patch series from Stephen Boyd is closely related:
> > https://lore.kernel.org/linux-arm-msm/20190910160903.65694-1-swboyd@xxxxxxxxxxxx/
> >
> > > The main use case I have is to map the command-db memory region on
> > > Qualcomm devices with a read-only mapping. It's already a const marked
> > > pointer and the API returns const pointers as well, so this series
> > > makes sure that even stray writes can't modify the memory.
> >
> > Stephen, what was the end result of that patch series? Mapping the
> > cmd-db read-only sounds cleaner than trying to be lucky with the right
> > set of cache flags.
> >
> 
> I dropped it because I got busy with other stuff. Feel free to pick it
> back up. It looks like the part where I left off was where we had to
> make the API fallback to mapping the memory as writeable if read-only
> isn't supported on the architecture.
[...]
> The other weird thing was that we passed both MEMREMAP_RO and
> MEMREMAP_WB to indicate what sort of fallback we want. Perhaps that can
> be encoded in the architecture layer so that you get the closest thing
> to read-only memory (i.e. any sort of write side caching is removed) and
> you don't have to pass a fallback mapping type.

Was there any motivation for having the fallback? I suspect driver
owners that want to use MEMREMAP_RO will know which architectures the
driver is applicable to and also know whether MEMREMAP_RO would work.

> I also wanted to return a const pointer.

The stash looks mostly complete. Do you think it should be part of the
series or submitted separately?

> 
> Here's my stash patch on top of the branch (from 2019!).
> 
> ---8<----
> From: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Date: Tue, 14 May 2019 13:22:01 -0700
> Subject: [PATCH] stash const iounmap
> 
> ---
>  arch/arm64/include/asm/io.h   |  2 +-
>  arch/arm64/mm/ioremap.c       |  9 +++++----
>  arch/x86/mm/ioremap.c         |  2 +-
>  drivers/firmware/google/vpd.c | 22 +++++++++++-----------
>  drivers/soc/qcom/rmtfs_mem.c  |  5 ++---
>  include/asm-generic/io.h      |  2 +-
>  include/linux/io.h            |  2 +-
>  include/linux/mmiotrace.h     |  2 +-
>  kernel/iomem.c                |  2 +-
>  9 files changed, 24 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index 245bd371e8dc..0fd4f1678300 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -178,7 +178,7 @@ extern void __memset_io(volatile void __iomem *,
> int, size_t);
>   * I/O memory mapping functions.
>   */
>  extern void __iomem *__ioremap(phys_addr_t phys_addr, size_t size,
> pgprot_t prot);
> -extern void __iounmap(volatile void __iomem *addr);
> +extern void __iounmap(const volatile void __iomem *addr);
>  extern void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size);
> 
>  #define ioremap(addr, size)		__ioremap((addr), (size),
> __pgprot(PROT_DEVICE_nGnRE))
> diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
> index c4c8cd4c31d4..e39fb2cb6042 100644
> --- a/arch/arm64/mm/ioremap.c
> +++ b/arch/arm64/mm/ioremap.c
> @@ -80,16 +80,17 @@ void __iomem *__ioremap(phys_addr_t phys_addr,
> size_t size, pgprot_t prot)
>  }
>  EXPORT_SYMBOL(__ioremap);
> 
> -void __iounmap(volatile void __iomem *io_addr)
> +void __iounmap(const volatile void __iomem *io_addr)
>  {
> -	unsigned long addr = (unsigned long)io_addr & PAGE_MASK;
> +	const unsigned long addr = (const unsigned long)io_addr & PAGE_MASK;
> +	const void *vaddr = (const void __force *)addr;
> 
>  	/*
>  	 * We could get an address outside vmalloc range in case
>  	 * of ioremap_cache() reusing a RAM mapping.
>  	 */
> -	if (is_vmalloc_addr((void *)addr))
> -		vunmap((void *)addr);
> +	if (is_vmalloc_addr(vaddr))
> +		vunmap(vaddr);
>  }
>  EXPORT_SYMBOL(__iounmap);
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 0029604af8a4..e9a2910d0c63 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -392,7 +392,7 @@ EXPORT_SYMBOL(ioremap_prot);
>   *
>   * Caller must ensure there is only one unmapping for the same pointer.
>   */
> -void iounmap(volatile void __iomem *addr)
> +void iounmap(const volatile void __iomem *addr)
>  {
>  	struct vm_struct *p, *o;
> 
> diff --git a/drivers/firmware/google/vpd.c b/drivers/firmware/google/vpd.c
> index c0c0b4e4e281..7428f189999e 100644
> --- a/drivers/firmware/google/vpd.c
> +++ b/drivers/firmware/google/vpd.c
> @@ -48,7 +48,7 @@ struct vpd_section {
>  	const char *name;
>  	char *raw_name;                /* the string name_raw */
>  	struct kobject *kobj;          /* vpd/name directory */
> -	char *baseaddr;
> +	const char *baseaddr;
>  	struct bin_attribute bin_attr; /* vpd/name_raw bin_attribute */
>  	struct list_head attribs;      /* key/value in vpd_attrib_info list */
>  };
> @@ -187,19 +187,19 @@ static int vpd_section_create_attribs(struct
> vpd_section *sec)
>  	return 0;
>  }
> 
> -static int vpd_section_init(const char *name, struct vpd_section *sec,
> +static int vpd_section_init(struct device *dev, const char *name,
> struct vpd_section *sec,
>  			    phys_addr_t physaddr, size_t size)
>  {
>  	int err;
> 
> -	sec->baseaddr = memremap(physaddr, size, MEMREMAP_WB);
> -	if (!sec->baseaddr)
> -		return -ENOMEM;
> +	sec->baseaddr = devm_memremap(physaddr, size, MEMREMAP_RO | MEMREMAP_WB);
> +	if (IS_ERR(sec->baseaddr))
> +		return PTR_ERR(sec->baseaddr);
> 
>  	sec->name = name;
> 
>  	/* We want to export the raw partition with name ${name}_raw */
> -	sec->raw_name = kasprintf(GFP_KERNEL, "%s_raw", name);
> +	sec->raw_name = devm_kasprintf(GFP_KERNEL, "%s_raw", name);
>  	if (!sec->raw_name) {
>  		err = -ENOMEM;
>  		goto err_memunmap;
> @@ -252,11 +252,12 @@ static int vpd_section_destroy(struct vpd_section *sec)
>  	return 0;
>  }
> 
> -static int vpd_sections_init(phys_addr_t physaddr)
> +static int vpd_sections_init(struct coreboot_device *cdev)
>  {
>  	struct vpd_cbmem __iomem *temp;
>  	struct vpd_cbmem header;
>  	int ret = 0;
> +	phys_addr_t physaddr = cdev->cbmem_ref.cbmem_addr;
> 
>  	temp = memremap(physaddr, sizeof(struct vpd_cbmem), MEMREMAP_WB);
>  	if (!temp)
> @@ -269,7 +270,7 @@ static int vpd_sections_init(phys_addr_t physaddr)
>  		return -ENODEV;
> 
>  	if (header.ro_size) {
> -		ret = vpd_section_init("ro", &ro_vpd,
> +		ret = vpd_section_init(&cdev->dev, "ro", &ro_vpd,
>  				       physaddr + sizeof(struct vpd_cbmem),
>  				       header.ro_size);
>  		if (ret)
> @@ -294,10 +295,9 @@ static int vpd_probe(struct coreboot_device *dev)
>  	int ret;
> 
>  	vpd_kobj = kobject_create_and_add("vpd", firmware_kobj);
> -	if (!vpd_kobj)
> -		return -ENOMEM;
> +	if (!vpd_kobj) return -ENOMEM;
> 
> -	ret = vpd_sections_init(dev->cbmem_ref.cbmem_addr);
> +	ret = vpd_sections_init(dev);
>  	if (ret) {
>  		kobject_put(vpd_kobj);
>  		return ret;
> diff --git a/drivers/soc/qcom/rmtfs_mem.c b/drivers/soc/qcom/rmtfs_mem.c
> index 6f5e8be9689c..137e5240d916 100644
> --- a/drivers/soc/qcom/rmtfs_mem.c
> +++ b/drivers/soc/qcom/rmtfs_mem.c
> @@ -212,10 +212,9 @@ static int qcom_rmtfs_mem_probe(struct
> platform_device *pdev)
>  	rmtfs_mem->dev.groups = qcom_rmtfs_mem_groups;
>  	rmtfs_mem->dev.release = qcom_rmtfs_mem_release_device;
> 
> -	rmtfs_mem->base = devm_memremap(&rmtfs_mem->dev, rmtfs_mem->addr,
> -					rmtfs_mem->size, MEMREMAP_WC);
> +	rmtfs_mem->base = devm_memremap_reserved_mem(&pdev->dev,
> +						     MEMREMAP_WC);
>  	if (IS_ERR(rmtfs_mem->base)) {
> -		dev_err(&pdev->dev, "failed to remap rmtfs_mem region\n");
>  		ret = PTR_ERR(rmtfs_mem->base);
>  		goto put_device;
>  	}
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> index 303871651f8a..d675a574eeb3 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -982,7 +982,7 @@ static inline void __iomem *__ioremap(phys_addr_t
> offset, size_t size,
>  #ifndef iounmap
>  #define iounmap iounmap
> 
> -static inline void iounmap(void __iomem *addr)
> +static inline void iounmap(const void __iomem *addr)
>  {
>  }
>  #endif
> diff --git a/include/linux/io.h b/include/linux/io.h
> index 16c7f4498869..82e6c4d6bdd3 100644
> --- a/include/linux/io.h
> +++ b/include/linux/io.h
> @@ -163,7 +163,7 @@ enum {
>  };
> 
>  void *memremap(resource_size_t offset, size_t size, unsigned long flags);
> -void memunmap(void *addr);
> +void memunmap(const void *addr);
> 
>  /*
>   * On x86 PAT systems we have memory tracking that keeps track of
> diff --git a/include/linux/mmiotrace.h b/include/linux/mmiotrace.h
> index 88236849894d..04607c468b73 100644
> --- a/include/linux/mmiotrace.h
> +++ b/include/linux/mmiotrace.h
> @@ -47,7 +47,7 @@ extern int kmmio_handler(struct pt_regs *regs,
> unsigned long addr);
>  /* Called from ioremap.c */
>  extern void mmiotrace_ioremap(resource_size_t offset, unsigned long size,
>  							void __iomem *addr);
> -extern void mmiotrace_iounmap(volatile void __iomem *addr);
> +extern void mmiotrace_iounmap(const volatile void __iomem *addr);
> 
>  /* For anyone to insert markers. Remember trailing newline. */
>  extern __printf(1, 2) int mmiotrace_printk(const char *fmt, ...);
> diff --git a/kernel/iomem.c b/kernel/iomem.c
> index 8d3cf74a32cb..22d0fa336360 100644
> --- a/kernel/iomem.c
> +++ b/kernel/iomem.c
> @@ -130,7 +130,7 @@ void *memremap(resource_size_t offset, size_t
> size, unsigned long flags)
>  }
>  EXPORT_SYMBOL(memremap);
> 
> -void memunmap(void *addr)
> +void memunmap(const void *addr)
>  {
>  	if (is_vmalloc_addr(addr))
>  		iounmap((void __iomem *) addr);
> 
> base-commit: 9e98c678c2d6ae3a17cb2de55d17f69dddaa231b
> prerequisite-patch-id: 62119e27c0c0686e02f0cb55c296b878fb7f5e47
> prerequisite-patch-id: bda32cfc1733c245ae3f141d7c27b18e4adcc628
> prerequisite-patch-id: b8f8097161bd15e87d54dcfbfa67b9ca1abc7204
> prerequisite-patch-id: cd374fb6e39941b8613d213b4a75909749409d63
> prerequisite-patch-id: d8dbc8485a0f86353a314ab5c22fc92d8eac1cc0
> prerequisite-patch-id: e539621b0eccf82aabf9891de69c30398abf76a0
> prerequisite-patch-id: 59d60033b80dec940201edd5aefed22726122a37
> prerequisite-patch-id: 0d16b23cec20eaab7f45ee84fd8d2950657dc72e
> -- 
> https://chromeos.dev
>