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Tsirkin" To: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Cc: Linux Kernel Mailing List , Baoquan He , Sergio Lopez Pascual , "Somlo, Gabriel" , xiaolong.ye@intel.com Subject: Re: [PATCH v14 8/9] fw_cfg: write vmcoreinfo details Message-ID: <20180215203418-mutt-send-email-mst@kernel.org> References: <20180214141850.4017-1-marcandre.lureau@redhat.com> <20180214141850.4017-9-marcandre.lureau@redhat.com> <20180214214105-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Thu, 15 Feb 2018 18:35:37 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Thu, 15 Feb 2018 18:35:37 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mst@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 15, 2018 at 07:24:34PM +0100, Marc-Andr? Lureau wrote: > Hi > > On Thu, Feb 15, 2018 at 7:09 PM, Michael S. Tsirkin wrote: > > On Wed, Feb 14, 2018 at 03:18:49PM +0100, Marc-Andr? Lureau wrote: > >> If the "etc/vmcoreinfo" fw_cfg file is present and we are not running > >> the kdump kernel, write the addr/size of the vmcoreinfo ELF note. > >> > >> The DMA operation is expected to run synchronously with today qemu, > >> but the specification states that it may become async, so we run > >> "control" field check in a loop for eventual changes. > >> > >> Signed-off-by: Marc-Andr? Lureau > >> --- > >> drivers/firmware/qemu_fw_cfg.c | 144 ++++++++++++++++++++++++++++++++++++++++- > >> 1 file changed, 141 insertions(+), 3 deletions(-) > >> > >> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c > >> index 37638b95cb45..69939e2529f2 100644 > >> --- a/drivers/firmware/qemu_fw_cfg.c > >> +++ b/drivers/firmware/qemu_fw_cfg.c > >> @@ -34,11 +34,17 @@ > >> #include > >> #include > >> #include > >> +#include > >> +#include > >> +#include > >> > >> MODULE_AUTHOR("Gabriel L. Somlo "); > >> MODULE_DESCRIPTION("QEMU fw_cfg sysfs support"); > >> MODULE_LICENSE("GPL"); > >> > >> +/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */ > >> +static u32 fw_cfg_rev; > >> + > >> /* fw_cfg device i/o register addresses */ > >> static bool fw_cfg_is_mmio; > >> static phys_addr_t fw_cfg_p_base; > >> @@ -59,6 +65,65 @@ static inline u16 fw_cfg_sel_endianness(u16 key) > >> (u16 __force)cpu_to_le16(key); > >> } > >> > >> +static inline bool fw_cfg_dma_enabled(void) > >> +{ > >> + return (fw_cfg_rev & FW_CFG_VERSION_DMA) && fw_cfg_reg_dma; > >> +} > >> + > >> +/* qemu fw_cfg device is sync today, but spec says it may become async */ > >> +static void fw_cfg_wait_for_control(struct fw_cfg_dma_access *d) > >> +{ > >> + do { > >> + u32 ctrl = be32_to_cpu(READ_ONCE(d->control)); > >> + > >> + if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0) > >> + return; > >> + > >> + usleep_range(50, 100); > > > > I would just do cpu_relax() here. > > ok, I didn't know that one. > > > > >> + } while (true); Pls write for (;;) and not do - while (true). > >> + > >> + /* do not reorder the read to d->control */ > >> + rmb(); > > > > Hmm. I don't really understand the comment. > > Is this code ever reacheable? How does it help? > > I thought that's what you suggested in v13 review, but true, I should > replace the return with a break to reach it. Is that what you expect > too? I'd do it unconditionally after reading ctrl. > (my understanding is to make sure the READ_ONCE(control) in > wait_for_control happens before READ_ONCE(control) after in > dma_transfer) I expect you to understand memory-barriers.txt :) > > > >> +} > >> + > >> +static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control) > >> +{ > >> + phys_addr_t dma; > >> + struct fw_cfg_dma_access *d = NULL; > >> + ssize_t ret = length; > >> + > >> + d = kmalloc(sizeof(*d), GFP_KERNEL); > >> + if (!d) { > >> + ret = -ENOMEM; > >> + goto end; > >> + } > >> + > >> + /* fw_cfg device does not need IOMMU protection, so use physical addresses */ > >> + *d = (struct fw_cfg_dma_access) { > >> + .address = cpu_to_be64(address ? virt_to_phys(address) : 0), > >> + .length = cpu_to_be32(length), > >> + .control = cpu_to_be32(control) > >> + }; > >> + > >> + dma = virt_to_phys(d); > >> + > >> + iowrite32be((u64)dma >> 32, fw_cfg_reg_dma); > >> + /* force memory to sync before notifying device via MMIO */ > >> + wmb(); > >> + iowrite32be(dma, fw_cfg_reg_dma + 4); > >> + > >> + fw_cfg_wait_for_control(d); > >> + > >> + if (be32_to_cpu(READ_ONCE(d->control)) & FW_CFG_DMA_CTL_ERROR) { > >> + ret = -EIO; > >> + } > >> + > >> +end: > >> + kfree(d); > >> + > >> + return ret; > >> +} > >> + > >> /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */ > >> static inline void fw_cfg_read_blob(u16 key, > >> void *buf, loff_t pos, size_t count) > >> @@ -87,6 +152,47 @@ static inline void fw_cfg_read_blob(u16 key, > >> acpi_release_global_lock(glk); > >> } > >> > >> +#ifdef CONFIG_CRASH_CORE > >> +/* write chunk of given fw_cfg blob (caller responsible for sanity-check) */ > >> +static ssize_t fw_cfg_write_blob(u16 key, > >> + void *buf, loff_t pos, size_t count) > >> +{ > >> + u32 glk = -1U; > >> + acpi_status status; > >> + ssize_t ret = count; > >> + > >> + /* If we have ACPI, ensure mutual exclusion against any potential > >> + * device access by the firmware, e.g. via AML methods: > >> + */ > >> + status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk); > >> + if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) { > >> + /* Should never get here */ > >> + WARN(1, "%s: Failed to lock ACPI!\n", __func__); > >> + return -EINVAL; > >> + } > >> + > >> + mutex_lock(&fw_cfg_dev_lock); > >> + if (pos == 0) { > >> + ret = fw_cfg_dma_transfer(buf, count, key << 16 > >> + | FW_CFG_DMA_CTL_SELECT > >> + | FW_CFG_DMA_CTL_WRITE); > >> + } else { > >> + iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl); > >> + ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP); > >> + if (ret < 0) > >> + goto end; > >> + ret = fw_cfg_dma_transfer(buf, count, FW_CFG_DMA_CTL_WRITE); > >> + } > >> + > >> +end: > >> + mutex_unlock(&fw_cfg_dev_lock); > >> + > >> + acpi_release_global_lock(glk); > >> + > >> + return ret; > >> +} > >> +#endif /* CONFIG_CRASH_CORE */ > >> + > >> /* clean up fw_cfg device i/o */ > >> static void fw_cfg_io_cleanup(void) > >> { > >> @@ -185,9 +291,6 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev) > >> return 0; > >> } > >> > >> -/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */ > >> -static u32 fw_cfg_rev; > >> - > >> static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf) > >> { > >> return sprintf(buf, "%u\n", fw_cfg_rev); > >> @@ -210,6 +313,32 @@ struct fw_cfg_sysfs_entry { > >> struct list_head list; > >> }; > >> > >> +#ifdef CONFIG_CRASH_CORE > >> +static ssize_t fw_cfg_write_vmcoreinfo(const struct fw_cfg_file *f) > >> +{ > >> + static struct fw_cfg_vmcoreinfo *data; > >> + ssize_t ret; > >> + > >> + data = kmalloc(sizeof(struct fw_cfg_vmcoreinfo), GFP_KERNEL); > >> + if (!data) > >> + return -ENOMEM; > >> + > >> + *data = (struct fw_cfg_vmcoreinfo) { > >> + .guest_format = cpu_to_le16(FW_CFG_VMCOREINFO_FORMAT_ELF), > >> + .size = cpu_to_le32(VMCOREINFO_NOTE_SIZE), > >> + .paddr = cpu_to_le64(paddr_vmcoreinfo_note()) > >> + }; > >> + /* spare ourself reading host format support for now since we > >> + * don't know what else to format - host may ignore ours > >> + */ > >> + ret = fw_cfg_write_blob(be16_to_cpu(f->select), data, > >> + 0, sizeof(struct fw_cfg_vmcoreinfo)); > >> + > >> + kfree(data); > >> + return ret; > >> +} > >> +#endif /* CONFIG_CRASH_CORE */ > >> + > >> /* get fw_cfg_sysfs_entry from kobject member */ > >> static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj) > >> { > >> @@ -450,6 +579,15 @@ static int fw_cfg_register_file(const struct fw_cfg_file *f) > >> int err; > >> struct fw_cfg_sysfs_entry *entry; > >> > >> +#ifdef CONFIG_CRASH_CORE > >> + if (fw_cfg_dma_enabled() && > >> + strcmp(f->name, FW_CFG_VMCOREINFO_FILENAME) == 0 && > >> + !is_kdump_kernel()) { > >> + if (fw_cfg_write_vmcoreinfo(f) < 0) > >> + pr_warn("fw_cfg: failed to write vmcoreinfo"); > >> + } > >> +#endif > >> + > >> /* allocate new entry */ > >> entry = kzalloc(sizeof(*entry), GFP_KERNEL); > >> if (!entry) > >> -- > >> 2.16.1.73.g5832b7e9f2