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Tue, 24 Mar 2026 05:47:05 -0700 (PDT) X-Received: by 2002:a17:902:f60a:b0:2b0:9a61:9e9 with SMTP id d9443c01a7336-2b09a611475mr77425305ad.32.1774356425148; Tue, 24 Mar 2026 05:47:05 -0700 (PDT) Received: from fedora ([49.36.108.16]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b08353e94asm142658105ad.25.2026.03.24.05.47.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2026 05:47:04 -0700 (PDT) Date: Tue, 24 Mar 2026 18:16:59 +0530 From: Arun Menon To: Jarkko Sakkinen Cc: linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, Jason Gunthorpe , Peter Huewe Subject: Re: [RFC 3/4] tpm_crb: Implement command and response chunking logic Message-ID: References: <20260324071803.324774-1-armenon@redhat.com> <20260324071803.324774-4-armenon@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Mar 24, 2026 at 12:45:29PM +0200, Jarkko Sakkinen wrote: > On Tue, Mar 24, 2026 at 12:48:02PM +0530, Arun Menon wrote: > > Add support for sending and receiving TPM command data in chunks when > > the payload exceeds the physical size of the hardware MMIO window. > > > > This introduces the following changes: > > > > - crb_map_io(): Checks the device interface capability to determine if > > chunking is supported, setting the chunking_supported flag. It also > > stores the hardware's maximum response buffer size in priv->rsp_size. > > - crb_send(): Iteratively writes command chunks to the fixed priv->cmd > > MMIO window. It signals the TPM backend to process intermediate chunks > > using CRB_START_NEXT_CHUNK, and signals the final chunk to begin > > execution using CRB_START_INVOKE. > > - crb_recv(): Parses the expected response size from the initial TPM > > header. It then iteratively reads chunks from the fixed priv->rsp > > MMIO window into the destination buffer, advancing the buffer offset > > until the complete response is retrieved. > > > > Signed-off-by: Arun Menon > > This is also just description of wha this adds. I'd lessen the detail > and write a description that describes motivation and logic of the > change. It's a good test for author knowledge, as if you really get > the topic you can explain its gist. In addition, it can be reflected > to implementation (vs. the descriptions that are pseudocode in English) Sure, I will replace the commit message with motivation+logic instead of explaining the code step by step. > > Since this RFC and QEMU does not have the feature in release it is > good to polish stuff like this. > > > --- > > drivers/char/tpm/tpm_crb.c | 150 +++++++++++++++++++++++++++---------- > > 1 file changed, 109 insertions(+), 41 deletions(-) > > > > diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c > > index 10128d078245c..fb63cc3737253 100644 > > --- a/drivers/char/tpm/tpm_crb.c > > +++ b/drivers/char/tpm/tpm_crb.c > > @@ -104,11 +104,13 @@ struct crb_priv { > > u8 __iomem *cmd; > > u8 __iomem *rsp; > > u32 cmd_size; > > + u32 rsp_size; > > u32 smc_func_id; > > u32 __iomem *pluton_start_addr; > > u32 __iomem *pluton_reply_addr; > > u8 ffa_flags; > > u8 ffa_attributes; > > + bool chunking_supported; > > }; > > > > struct tpm2_crb_smc { > > @@ -368,38 +370,6 @@ static u8 crb_status(struct tpm_chip *chip) > > return sts; > > } > > > > -static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count) > > -{ > > - struct crb_priv *priv = dev_get_drvdata(&chip->dev); > > - unsigned int expected; > > - > > - /* A sanity check that the upper layer wants to get at least the header > > - * as that is the minimum size for any TPM response. > > - */ > > - if (count < TPM_HEADER_SIZE) > > - return -EIO; > > - > > - /* If this bit is set, according to the spec, the TPM is in > > - * unrecoverable condition. > > - */ > > - if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR) > > - return -EIO; > > - > > - /* Read the first 8 bytes in order to get the length of the response. > > - * We read exactly a quad word in order to make sure that the remaining > > - * reads will be aligned. > > - */ > > - memcpy_fromio(buf, priv->rsp, 8); > > - > > - expected = be32_to_cpup((__be32 *)&buf[2]); > > - if (expected > count || expected < TPM_HEADER_SIZE) > > - return -EIO; > > - > > - memcpy_fromio(&buf[8], &priv->rsp[8], expected - 8); > > - > > - return expected; > > -} > > - > > static int crb_do_acpi_start(struct tpm_chip *chip) > > { > > union acpi_object *obj; > > @@ -474,6 +444,8 @@ static int crb_trigger_tpm(struct tpm_chip *chip, u32 start_cmd) > > static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len) > > { > > struct crb_priv *priv = dev_get_drvdata(&chip->dev); > > + size_t offset = 0; > > + size_t chunk_size; > > int rc = 0; > > > > /* Zero the cancel register so that the next command will not get > > @@ -481,7 +453,7 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len) > > */ > > iowrite32(0, &priv->regs_t->ctrl_cancel); > > > > - if (len > priv->cmd_size) { > > + if (len > priv->cmd_size && !priv->chunking_supported) { > > dev_err(&chip->dev, "invalid command count value %zd %d\n", > > len, priv->cmd_size); > > return -E2BIG; > > @@ -491,16 +463,101 @@ static int crb_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz, size_t len) > > if (priv->sm == ACPI_TPM2_COMMAND_BUFFER_WITH_PLUTON) > > __crb_cmd_ready(&chip->dev, priv, chip->locality); > > > > - memcpy_toio(priv->cmd, buf, len); > > + while (offset < len) { > > + chunk_size = min_t(size_t, len - offset, priv->cmd_size); > > + > > + memcpy_toio(priv->cmd, buf + offset, chunk_size); > > + offset += chunk_size; > > + > > + /* Make sure that cmd is populated before issuing start. */ > > + wmb(); > > + if (offset < len) { > > + rc = crb_trigger_tpm(chip, CRB_START_NEXT_CHUNK); > > + if (rc) > > + return rc; > > + if (!crb_wait_for_reg_32(&priv->regs_t->ctrl_start, > > + CRB_START_NEXT_CHUNK, 0, TPM2_TIMEOUT_C)) { > > + dev_err(&chip->dev, > > + "Timeout waiting for backend to consume chunk\n"); > > + return -ETIME; > > + } > > + } else { > > + rc = crb_trigger_tpm(chip, CRB_START_INVOKE); > > + if (rc) > > + return rc; > > + } > > + } > > + return crb_try_pluton_doorbell(priv, false); > > +} > > > > - /* Make sure that cmd is populated before issuing start. */ > > - wmb(); > > +static int crb_recv(struct tpm_chip *chip, u8 *buf, size_t count) > > +{ > > + struct crb_priv *priv = dev_get_drvdata(&chip->dev); > > + unsigned int expected; > > + size_t offset = 0; > > + size_t chunk_size; > > + size_t first_read; > > + int rc; > > > > - rc = crb_trigger_tpm(chip, CRB_START_INVOKE); > > - if (rc) > > - return rc; > > + /* A sanity check that the upper layer wants to get at least the header > > + * as that is the minimum size for any TPM response. > > + */ > > + if (count < TPM_HEADER_SIZE) > > + return -EIO; > > > > - return crb_try_pluton_doorbell(priv, false); > > + /* If this bit is set, according to the spec, the TPM is in > > + * unrecoverable condition. > > + */ > > + if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR) > > + return -EIO; > > + > > + /* Read the first 8 bytes in order to get the length of the response. > > + * We read exactly a quad word in order to make sure that the remaining > > + * reads will be aligned. > > + */ > > + memcpy_fromio(buf, priv->rsp, 8); > > + > > + expected = be32_to_cpup((__be32 *)&buf[2]); > > + if (expected > count || expected < TPM_HEADER_SIZE) > > + return -EIO; > > + > > + /* > > + * Set chunk_size by comparing the size of the buffer that the upper layer has > > + * allocated (count) to the hardware tpm limit (priv->rsp_size). > > + * This is to prevent buffer overflow while writing to buf. > > + */ > > + chunk_size = min_t(size_t, count, priv->rsp_size); > > + > > + /* > > + * Compare the actual size of the response we found in the header to the chunk_size. > > + */ > > + first_read = min_t(size_t, expected, chunk_size); > > + > > + memcpy_fromio(&buf[8], &priv->rsp[8], first_read - 8); > > + offset = first_read; > > + > > + while (offset < expected) { > > + if (!priv->chunking_supported) { > > + dev_err(&chip->dev, "Response larger than MMIO and chunking not supported\n"); > > + return -EIO; > > + } > > + > > + rc = crb_trigger_tpm(chip, CRB_START_NEXT_CHUNK); > > + if (rc) > > + return rc; > > + > > + if (!crb_wait_for_reg_32(&priv->regs_t->ctrl_start, > > + CRB_START_NEXT_CHUNK, 0, TPM2_TIMEOUT_C)) { > > + dev_err(&chip->dev, "Timeout waiting for backend response\n"); > > + return -ETIME; > > + } > > + > > + chunk_size = min_t(size_t, expected - offset, priv->rsp_size); > > + memcpy_fromio(buf + offset, priv->rsp, chunk_size); > > + offset += chunk_size; > > + } > > + > > + return expected; > > } > > > > static void crb_cancel(struct tpm_chip *chip) > > @@ -727,6 +784,15 @@ static int crb_map_io(struct acpi_device *device, struct crb_priv *priv, > > goto out; > > } > > > > + if (priv->regs_h) { > > + u32 intf_id = ioread32((u32 __iomem *)&priv->regs_h->intf_id); > > + > > + if (intf_id & CRB_INTF_CAP_CRB_CHUNK) { > > + priv->chunking_supported = true; > > + dev_info(dev, "CRB Chunking is supported by backend\n"); > > + } > > + } > > + > > memcpy_fromio(&__rsp_pa, &priv->regs_t->ctrl_rsp_pa, 8); > > rsp_pa = le64_to_cpu(__rsp_pa); > > rsp_size = ioread32(&priv->regs_t->ctrl_rsp_size); > > @@ -764,8 +830,10 @@ static int crb_map_io(struct acpi_device *device, struct crb_priv *priv, > > priv->rsp = priv->cmd; > > > > out: > > - if (!ret) > > + if (!ret) { > > priv->cmd_size = cmd_size; > > + priv->rsp_size = rsp_size; > > + } > > > > __crb_go_idle(dev, priv, 0); > > > > -- > > 2.53.0 > > > > BR, Jarkko > Regards, Arun Menon