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[34.142.211.105]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-89f58017244sm3517077b3a.47.2026.10.19.01.18.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Oct 2026 01:18:16 -0700 (PDT) Date: Mon, 19 Oct 2026 08:18:08 +0000 From: Pranjal Shrivastava To: Thomas Gleixner Cc: iommu@lists.linux.dev, Will Deacon , Joerg Roedel , Robin Murphy , Jason Gunthorpe , Mostafa Saleh , Nicolin Chen , Daniel Mentz , Ashish Mhetre , linux-arm-kernel@lists.infradead.org, Radu Rendec , Bjorn Helgaas , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , rafael@kernel.org, Danilo Krummrich , driver-core@lists.linux.dev, sashiko-bot@kernel.org Subject: Re: [PATCH v11 07/16] genirq/msi: Cache MSI message in irq_chip_write_msi_msg() Message-ID: References: <20260929034510.2023173-1-praan@google.com> <20260929034510.2023173-8-praan@google.com> <875wz4eyqe.ffs@fw13> 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: <875wz4eyqe.ffs@fw13> On Wed, Oct 14, 2026 at 11:52:41PM +0200, Thomas Gleixner wrote: > On Tue, Sep 29 2026 at 03:45, Pranjal Shrivastava wrote: > > Currently, PCI MSI caches the composed MSI message into the MSI > > descriptor inside __pci_write_msi_msg(), whereas platform MSI and other > > device MSI domains do not cache the message in the core, forcing > > individual drivers to manually copy the message into desc->msg if they > > need to restore it across power transitions. > > > > Cache desc->msg in irq_chip_write_msi_msg() before invoking the chip > > callback so all hierarchical MSI domains automatically record the > > latest message. Document why the redundant assignment in > > __pci_write_msi_msg() must remain for direct callers outside the > > irq_chip hierarchy. > > > > Suggested-by: Thomas Gleixner > > Signed-off-by: Pranjal Shrivastava > > --- > > drivers/pci/msi/msi.c | 6 ++++++ > > kernel/irq/msi.c | 9 +++++++++ > > 2 files changed, 15 insertions(+) > > > > diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c > > index 80a9db417dc8..f7bedc31d486 100644 > > --- a/drivers/pci/msi/msi.c > > +++ b/drivers/pci/msi/msi.c > > @@ -257,6 +257,12 @@ void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg) > > pci_write_msg_msi(dev, entry, msg); > > } > > > > + /* > > + * Although irq_chip_write_msi_msg() already caches the message, > > + * keep the assignment here for callers that invoke > > + * __pci_write_msi_msg() or pci_write_msi_msg() directly outside > > + * the irq_chip hierarchy. > > + */ > > entry->msg = *msg; > > > > if (entry->write_msi_msg) > > diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c > > index fb5f372215bf..df460a574d80 100644 > > --- a/kernel/irq/msi.c > > +++ b/kernel/irq/msi.c > > @@ -634,6 +634,15 @@ static unsigned int msi_domain_get_hwsize(struct device *dev, unsigned int domid > > static inline void irq_chip_write_msi_msg(struct irq_data *data, > > struct msi_msg *msg) > > { > > + struct msi_desc *desc = irq_data_get_msi_desc(data); > > + > > + /* > > + * PCI Multi-MSI shares a single descriptor across all vectors and > > + * the device stores only the base message. Cache the message of the > > + * first interrupt only, so that sub-vectors cannot overwrite it. > > + */ > > + if (desc->irq == data->irq) > > + desc->msg = *msg; > > data->chip->irq_write_msi_msg(data, msg); > > } > > Sashiko reported correctly: > > > [Severity: Critical] > > Does this code cause a NULL pointer dereference for domains without an > > msi_desc object? > > So this needs to be: > > if (desc && desc->irq == data->irq) > desc->msg = *msg; > > Did not think about that, but that also means that this patch was not > tested on any recent (less than 10 years old) Intel x86 platform or a > x86 VM exposing HPET... > Ack, I'll fix that, and yes, I've tested this on arm64 platforms only. I'll pick up a recent Intel x86 platform as well, to test this. > Thanks, > > tglx > > Thanks, Praan