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Date: Fri, 11 Dec 2020 11:25:18 -0800 From: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> To: Thiago Jung Bauermann <bauerman@...ux.ibm.com> Cc: zohar@...ux.ibm.com, robh@...nel.org, gregkh@...uxfoundation.org, james.morse@....com, catalin.marinas@....com, sashal@...nel.org, will@...nel.org, mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org, robh+dt@...nel.org, frowand.list@...il.com, vincenzo.frascino@....com, mark.rutland@....com, dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com, pasha.tatashin@...een.com, allison@...utok.net, kstewart@...uxfoundation.org, takahiro.akashi@...aro.org, tglx@...utronix.de, masahiroy@...nel.org, bhsharma@...hat.com, mbrugger@...e.com, hsinyi@...omium.org, tao.li@...o.com, christophe.leroy@....fr, linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, prsriva@...ux.microsoft.com, balajib@...ux.microsoft.com Subject: Re: [PATCH v10 2/8] powerpc: Move delete_fdt_mem_rsv() to drivers/of/kexec.c On 12/11/20 10:19 AM, Thiago Jung Bauermann wrote: > > Hi Lakshmi, > > Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> writes: > >> On 12/6/20 5:50 PM, Lakshmi Ramasubramanian wrote: >> >> Hi Thiago, >> >>> On 12/4/20 6:22 PM, Thiago Jung Bauermann wrote >>>> >>>> Hello Lakshmi, >>>> >>>> Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> writes: >>>> >>>>> delete_fdt_mem_rsv() retrieves the memory reserve map entry, for >>>>> the given starting address and size, from the device tree blob, and >>>>> removes the entry from the device tree blob. This function is called >>>>> to free the resources reserved for the buffer used for carrying forward >>>>> the IMA measurement logs on kexec. This function does not have >>>>> architecture specific code, but is currently limited to powerpc. >>>>> >>>>> Move delete_fdt_mem_rsv() to "drivers/of/kexec_fdt.c" so that it is >>>> >>>> s/kexec_fdt.c/kexec.c/ >>> Missed that in the patch description. Will fix it. Thanks. >>> >>>>> accessible for other architectures as well. >>>>> >>>>> Co-developed-by: Prakhar Srivastava <prsriva@...ux.microsoft.com> >>>>> Signed-off-by: Prakhar Srivastava <prsriva@...ux.microsoft.com> >>>>> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> >>>>> --- >>>>> arch/powerpc/include/asm/kexec.h | 1 - >>>>> arch/powerpc/kexec/file_load.c | 32 ----------------- >>>>> drivers/of/Makefile | 1 + >>>>> drivers/of/kexec.c | 61 ++++++++++++++++++++++++++++++++ >>>>> include/linux/kexec.h | 5 +++ >>>>> 5 files changed, 67 insertions(+), 33 deletions(-) >>>>> create mode 100644 drivers/of/kexec.c >>>>> >>>>> diff --git a/arch/powerpc/include/asm/kexec.h >>>>> b/arch/powerpc/include/asm/kexec.h >>>>> index 55d6ede30c19..7c223031ecdd 100644 >>>>> --- a/arch/powerpc/include/asm/kexec.h >>>>> +++ b/arch/powerpc/include/asm/kexec.h >>>>> @@ -126,7 +126,6 @@ int setup_purgatory(struct kimage *image, const void >>>>> *slave_code, >>>>> int setup_new_fdt(const struct kimage *image, void *fdt, >>>>> unsigned long initrd_load_addr, unsigned long initrd_len, >>>>> const char *cmdline); >>>>> -int delete_fdt_mem_rsv(void *fdt, unsigned long start, unsigned long size); >>>>> #ifdef CONFIG_PPC64 >>>>> struct kexec_buf; >>>>> diff --git a/arch/powerpc/kexec/file_load.c b/arch/powerpc/kexec/file_load.c >>>>> index 9a232bc36c8f..9efc98b1e2ae 100644 >>>>> --- a/arch/powerpc/kexec/file_load.c >>>>> +++ b/arch/powerpc/kexec/file_load.c >>>>> @@ -109,38 +109,6 @@ int setup_purgatory(struct kimage *image, const void >>>>> *slave_code, >>>>> return 0; >>>>> } >>>>> -/** >>>>> - * delete_fdt_mem_rsv - delete memory reservation with given address and >>>>> size >>>>> - * >>>>> - * Return: 0 on success, or negative errno on error. >>>>> - */ >>>>> -int delete_fdt_mem_rsv(void *fdt, unsigned long start, unsigned long size) >>>>> -{ >>>>> - int i, ret, num_rsvs = fdt_num_mem_rsv(fdt); >>>>> - >>>>> - for (i = 0; i < num_rsvs; i++) { >>>>> - uint64_t rsv_start, rsv_size; >>>>> - >>>>> - ret = fdt_get_mem_rsv(fdt, i, &rsv_start, &rsv_size); >>>>> - if (ret) { >>>>> - pr_err("Malformed device tree.\n"); >>>>> - return -EINVAL; >>>>> - } >>>>> - >>>>> - if (rsv_start == start && rsv_size == size) { >>>>> - ret = fdt_del_mem_rsv(fdt, i); >>>>> - if (ret) { >>>>> - pr_err("Error deleting device tree reservation.\n"); >>>>> - return -EINVAL; >>>>> - } >>>>> - >>>>> - return 0; >>>>> - } >>>>> - } >>>>> - >>>>> - return -ENOENT; >>>>> -} >>>>> - >>>>> /* >>>>> * setup_new_fdt - modify /chosen and memory reservation for the next >>>>> kernel >>>>> * @image: kexec image being loaded. >>>>> diff --git a/drivers/of/Makefile b/drivers/of/Makefile >>>>> index 6e1e5212f058..77d24712c0c8 100644 >>>>> --- a/drivers/of/Makefile >>>>> +++ b/drivers/of/Makefile >>>>> @@ -13,5 +13,6 @@ obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o >>>>> obj-$(CONFIG_OF_RESOLVE) += resolver.o >>>>> obj-$(CONFIG_OF_OVERLAY) += overlay.o >>>>> obj-$(CONFIG_OF_NUMA) += of_numa.o >>>>> +obj-$(CONFIG_OF_FLATTREE) += kexec.o >>>> >>>> Isn't this too broad? kexec.o will only be useful to kernel configs >>>> which enable CONFIG_KEXEC_FILE, so perhaps do: >>>> >>>> ifdef CONFIG_OF_FLATTREE >>>> ifdef CONFIG_KEXEC_FILE >>>> obj-y += kexec.o >>>> endif >>>> endif >>>> >>>> What do you think? >>> Per Rob's feedback on v9 patch set, I have moved all the architecture >>> independent ima kexec functions to a single file "drivers/of/kexec.c" >>> Since these functions are enabled on different kernel CONFIGs, I have >>> used IS_ENABLED(CONFIG_XYZ) macro instead of "#ifdef" in the C file to >>> conditionally compile. >> Per Rob's feedback on the v9 patch, I'll keep the ima kexec functions in a >> single file (in "drivers/of/kexec.c") and use IS_ENABLED() macro to handle the >> function calls. >> >> I'll make the other changes you'd suggested on v10 patches and will post v11 >> patch set shortly. > >>>From a cursory look at the use of functions in this file, I got the > impression that there wouldn't be any reference to them in kernel > configs that didn't have CONFIG_KEXEC_FILE enabled, which is why I > suggested the change above. I think you can make it without any other > changes to the code. > > I could be wrong though, and there could be some config which tried to > use some of these functions even when CONFIG_KEXEC_FILE is disabled. In > that case, the customary way to resolve it is to provide static inline > stub versions in a header file (not in a .c file) of just those > functions that are needed. > > The reason why placing stub functions in header files is better is that > then the compiler has visibility of the dummy function when compiling > the source file which uses the function, and is able to eliminate the > dead code that arises from the function always returning one value. I agree with you Thiago. Is there a way to keep all the relevant functions in a single C file, not use "#ifdef" in C file, and follow the coding pattern you've described above (i mean, "defining a stub function in a header file when the config conditions are not met")? > > Using IS_ENABLED() to do an early return as the first operation in the > function in a separate .c file means that the compiler doesn't know > anything and has to put a jump to the dummy function (only to > immediately return), and retain the code that deals with the possibility > of different values being returned. > > It's not a big deal in this case because none of these functions is in a > hot path, but it does make the kernel text a tiny bit bigger than > necessary. > I agree. thanks, -lakshmi
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