From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0594E28B50B; Tue, 22 Jul 2025 23:23:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753226582; cv=none; b=VgX5q6fyRG7aHUbq4j/6w1iX8LdfXZiyul+DQtUZqeQD9yz7l48wbyAeyOxgvZZQifMKXxcp0V1UjuOA3jPNPS/ZaulfQGEaEKmU6LjVegwHGuwbmf4xOhWrabP0nBLX2PpJ/jzAHw2D2wXkk4mnegMgaJfE4dSQ3ldKdDsBbrA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753226582; c=relaxed/simple; bh=HBLhn20/CLD1HW+c4eQLNkCqvP+zMCJHSADkazYo/TE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HJUksgj8AKn1hrZ+qsfiD9mzgRVRbvXrv2lAQqwOKwnsifcsJTlJ8VN2w58Hou99SVzLmSYrBe0sOOrRG71Fc06ElSugohUpDvwrZVKPXBR9jG5C4xOa7H8BKsFZna6PJKbCNYbm0ABkWZ8gNHY/MUEnNXdCiJS5vw50zbqLxME= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mSlFjeEQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mSlFjeEQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AB14C4CEEB; Tue, 22 Jul 2025 23:23:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753226581; bh=HBLhn20/CLD1HW+c4eQLNkCqvP+zMCJHSADkazYo/TE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mSlFjeEQyq0Iya5iWLRfZDWYFkgzzHRZg13eVHUniYERawrujSVB3lP0GvqyePOEG gJv3hipmL+P8tlQQNlhn+OXTZdrB8zsSO5ziEIrIDMgreAEfl6vJIPX8jNzd1BbwRi jj5RR0dqYNtq+232GTfHu8A4H9T1Fe/CSjFqbSVssfti+tdmImi2bkdmopoFe6bpPq 2lKmghEbpafXFRVQb3ilSVACCd4z/pe1XQ0jqZuSQKX0BlXQawJUHRb9dIs1hC5XfU IrScIcrQ2P1XzJAJfI2v9jd0WNZResdGQYBS34rzJkHRKojmhcCmgBpDg/fclRLQj2 nS8Fu+z4DQYTQ== Date: Wed, 23 Jul 2025 02:22:57 +0300 From: Jarkko Sakkinen To: Ivan Orlov Cc: peterhuewe@gmx.de, iorlov@amazon.co.uk, jgg@ziepe.ca, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, dwmw@amazon.co.uk, noodles@earth.li Subject: Re: [PATCH v3] tpm: Check for completion after timeout Message-ID: References: <20250719201340.24447-1-ivan.orlov0322@gmail.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 Wed, Jul 23, 2025 at 02:18:52AM +0300, Jarkko Sakkinen wrote: > On Sat, Jul 19, 2025 at 08:13:39PM +0000, Ivan Orlov wrote: > > The current implementation of timeout detection works in the following > > way: > > > > 1. Read completion status. If completed, return the data > > 2. Sleep for some time (usleep_range) > > 3. Check for timeout using current jiffies value. Return an error if > > timed out > > 4. Goto 1 > > > > usleep_range doesn't guarantee it's always going to wake up strictly in > > (min, max) range, so such a situation is possible: > > > > 1. Driver reads completion status. No completion yet > > 2. Process sleeps indefinitely. In the meantime, TPM responds > > 3. We check for timeout without checking for the completion again. > > Result is lost. > > > > Such a situation also happens for the guest VMs: if vCPU goes to sleep > > and doesn't get scheduled for some time, the guest TPM driver will > > timeout instantly after waking up without checking for the completion > > (which may already be in place). > > > > Perform the completion check once again after exiting the busy loop in > > order to give the device the last chance to send us some data. > > > > Since now we check for completion in two places, extract this check into > > a separate function. > > > > Signed-off-by: Ivan Orlov > > --- > > V1 -> V2: > > - Exclude the jiffies -> ktime change from the patch > > - Instead of recording the time before checking for completion, check > > for completion once again after leaving the loop > > V2 -> V3: > > - Avoid reading the chip status twice in the inner loop by passing > > status into tpm_transmit_completed > > > > drivers/char/tpm/tpm-interface.c | 17 +++++++++++++++-- > > 1 file changed, 15 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c > > index 8d7e4da6ed53..8d18b33aa62d 100644 > > --- a/drivers/char/tpm/tpm-interface.c > > +++ b/drivers/char/tpm/tpm-interface.c > > @@ -82,6 +82,13 @@ static bool tpm_chip_req_canceled(struct tpm_chip *chip, u8 status) > > return chip->ops->req_canceled(chip, status); > > } > > > > +static bool tpm_transmit_completed(u8 status, struct tpm_chip *chip) > > +{ > > + u8 status_masked = status & chip->ops->req_complete_mask; > > + > > + return status_masked == chip->ops->req_complete_val; > > +} > > + > > static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz) > > { > > struct tpm_header *header = buf; > > @@ -129,8 +136,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz) > > stop = jiffies + tpm_calc_ordinal_duration(chip, ordinal); > > do { > > u8 status = tpm_chip_status(chip); > > - if ((status & chip->ops->req_complete_mask) == > > - chip->ops->req_complete_val) > > + if (tpm_transmit_completed(status, chip)) > > goto out_recv; > > > > if (tpm_chip_req_canceled(chip, status)) { > > @@ -142,6 +148,13 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz) > > rmb(); > > } while (time_before(jiffies, stop)); > > > > + /* > > + * Check for completion one more time, just in case the device reported > > + * it while the driver was sleeping in the busy loop above. > > + */ > > + if (tpm_transmit_completed(tpm_chip_status(chip), chip)) > > + goto out_recv; > > + > > tpm_chip_cancel(chip); > > dev_err(&chip->dev, "Operation Timed out\n"); > > return -ETIME; > > -- > > 2.43.0 > > > > I guess this is completed too by now ... > > Reviewed-by: Jarkko Sakkinen Just saying (i.e. I will fix it up): s/Reviewed-By/Reviewed-by/g ;-) checkpatch.pl does scream about this but yeah not a huge deal! BR, Jarkko