linux-kernel - [PATCH v4] PCI: Align pci memory space base address with page size

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Date:   Fri,  9 Jun 2023 10:20:47 +0800
From:   Bibo Mao <maobibo@...ngson.cn>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Huacai Chen <chenhuacai@...nel.org>,
        Will Deacon <will@...nel.org>, loongarch@...ts.linux.dev,
        loongson-kernel@...ts.loongnix.cn
Subject: [PATCH v4] PCI: Align pci memory space base address with page size

Some PCI devices have only 4K memory space size, it is normal in general
machines and aligned with page size. However some architectures which
support different page size, default page size on LoongArch is 16K, and
ARM64 supports page size varying from 4K to 64K. On machines where larger
page size is use, memory space region of two different pci devices may be
in one page. It is not safe with mmu protection, also VFIO pci device
driver requires base address of pci memory space page aligned, so that it
can be memory mapped to qemu user space when it is passed-through to vm.

It consumes more pci memory resource with page size alignment requirement,
here extra option PCI_MEMRES_PAGE_ALIGN is added, it can be enabled by
different architectures.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
Change history
v4: add extra kernel option PCI_MEMRES_PAGE_ALIGN to set memory resource
    page aligned.

v3: move alignment requirement to generic pci code

v2: add pci resource alignment requirement in arch specified function
    pcibios_align_resource on arm64/LoongArch platforms

---
 arch/loongarch/Kconfig  | 1 +
 drivers/pci/Kconfig     | 3 +++
 drivers/pci/setup-res.c | 7 +++++++
 3 files changed, 11 insertions(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index d38b066fc931..65b2f6ba9f8e 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -142,6 +142,7 @@ config LOONGARCH
 	select PCI_LOONGSON
 	select PCI_MSI_ARCH_FALLBACKS
 	select PCI_QUIRKS
+	select PCI_MEMRES_PAGE_ALIGN
 	select PERF_USE_VMALLOC
 	select RTC_LIB
 	select SMP
diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 9309f2469b41..9be5f85ff9dc 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -128,6 +128,9 @@ config PCI_LOCKLESS_CONFIG
 config PCI_BRIDGE_EMUL
 	bool
 
+config PCI_MEMRES_PAGE_ALIGN
+	bool
+
 config PCI_IOV
 	bool "PCI IOV support"
 	select PCI_ATS
diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index 967f9a758923..6ad76734a670 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -339,6 +339,13 @@ int pci_assign_resource(struct pci_dev *dev, int resno)
 		return -EINVAL;
 	}
 
+#ifdef CONFIG_PCI_MEMRES_PAGE_ALIGN
+	/*
+	 * force minimum page alignment for vfio pci usage
+	 */
+	if (res->flags & IORESOURCE_MEM)
+		align = max_t(resource_size_t, PAGE_SIZE, align);
+#endif
 	size = resource_size(res);
 	ret = _pci_assign_resource(dev, resno, size, align);
 
-- 
2.27.0