Nouveau - May 2023 - [PATCH 2/4] x86: always initialize xen-swiotlb when xen-pcifront is enabling

Remove the dangerous late initialization of xen-swiotlb in
pci_xen_swiotlb_init_late and instead just always initialize
xen-swiotlb in the boot code if CONFIG_XEN_PCIDEV_FRONTEND is enabled.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 arch/x86/include/asm/xen/swiotlb-xen.h |  6 ------
 arch/x86/kernel/pci-dma.c              | 25 +++----------------------
 drivers/pci/xen-pcifront.c             |  6 ------
 3 files changed, 3 insertions(+), 34 deletions(-)

diff --git a/arch/x86/include/asm/xen/swiotlb-xen.h
b/arch/x86/include/asm/xen/swiotlb-xen.h
index 77a2d19cc9909e..abde0f44df57dc 100644
--- a/arch/x86/include/asm/xen/swiotlb-xen.h
+++ b/arch/x86/include/asm/xen/swiotlb-xen.h
@@ -2,12 +2,6 @@
 #ifndef _ASM_X86_SWIOTLB_XEN_H
 #define _ASM_X86_SWIOTLB_XEN_H
 
-#ifdef CONFIG_SWIOTLB_XEN
-extern int pci_xen_swiotlb_init_late(void);
-#else
-static inline int pci_xen_swiotlb_init_late(void) { return -ENXIO; }
-#endif
-
 int xen_swiotlb_fixup(void *buf, unsigned long nslabs);
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
 				unsigned int address_bits,
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index f887b08ac5ffe4..c4a7ead9eb674e 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -81,27 +81,6 @@ static void __init pci_xen_swiotlb_init(void)
 	if (IS_ENABLED(CONFIG_PCI))
 		pci_request_acs();
 }
-
-int pci_xen_swiotlb_init_late(void)
-{
-	if (dma_ops == &xen_swiotlb_dma_ops)
-		return 0;
-
-	/* we can work with the default swiotlb */
-	if (!io_tlb_default_mem.nslabs) {
-		int rc = swiotlb_init_late(swiotlb_size_or_default(),
-					   GFP_KERNEL, xen_swiotlb_fixup);
-		if (rc < 0)
-			return rc;
-	}
-
-	/* XXX: this switches the dma ops under live devices! */
-	dma_ops = &xen_swiotlb_dma_ops;
-	if (IS_ENABLED(CONFIG_PCI))
-		pci_request_acs();
-	return 0;
-}
-EXPORT_SYMBOL_GPL(pci_xen_swiotlb_init_late);
 #else
 static inline void __init pci_xen_swiotlb_init(void)
 {
@@ -111,7 +90,9 @@ static inline void __init pci_xen_swiotlb_init(void)
 void __init pci_iommu_alloc(void)
 {
 	if (xen_pv_domain()) {
-		if (xen_initial_domain() || x86_swiotlb_enable)
+		if (xen_initial_domain() ||
+		    IS_ENABLED(CONFIG_XEN_PCIDEV_FRONTEND) ||
+		    x86_swiotlb_enable)
 			pci_xen_swiotlb_init();
 		return;
 	}
diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
index 83c0ab50676dff..11636634ae512f 100644
--- a/drivers/pci/xen-pcifront.c
+++ b/drivers/pci/xen-pcifront.c
@@ -22,7 +22,6 @@
 #include <linux/bitops.h>
 #include <linux/time.h>
 #include <linux/ktime.h>
-#include <linux/swiotlb.h>
 #include <xen/platform_pci.h>
 
 #include <asm/xen/swiotlb-xen.h>
@@ -669,11 +668,6 @@ static int pcifront_connect_and_init_dma(struct
pcifront_device *pdev)
 
 	spin_unlock(&pcifront_dev_lock);
 
-	if (!err && !is_swiotlb_active(&pdev->xdev->dev)) {
-		err = pci_xen_swiotlb_init_late();
-		if (err)
-			dev_err(&pdev->xdev->dev, "Could not setup SWIOTLB!\n");
-	}
 	return err;
 }
 
-- 
2.39.2

On Thu, May 18, 2023 at 03:42:51PM +0200, Christoph Hellwig
wrote:
> Remove the dangerous late initialization of xen-swiotlb in
> pci_xen_swiotlb_init_late and instead just always initialize
> xen-swiotlb in the boot code if CONFIG_XEN_PCIDEV_FRONTEND is enabled.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
Doesn't it mean all the PV guests will basically waste 64MB of RAM
by default each if they don't really have PCI devices?
> ---
>  arch/x86/include/asm/xen/swiotlb-xen.h |  6 ------
>  arch/x86/kernel/pci-dma.c              | 25 +++----------------------
>  drivers/pci/xen-pcifront.c             |  6 ------
>  3 files changed, 3 insertions(+), 34 deletions(-)
> 
> diff --git a/arch/x86/include/asm/xen/swiotlb-xen.h
b/arch/x86/include/asm/xen/swiotlb-xen.h
> index 77a2d19cc9909e..abde0f44df57dc 100644
> --- a/arch/x86/include/asm/xen/swiotlb-xen.h
> +++ b/arch/x86/include/asm/xen/swiotlb-xen.h
> @@ -2,12 +2,6 @@
>  #ifndef _ASM_X86_SWIOTLB_XEN_H
>  #define _ASM_X86_SWIOTLB_XEN_H
>  
> -#ifdef CONFIG_SWIOTLB_XEN
> -extern int pci_xen_swiotlb_init_late(void);
> -#else
> -static inline int pci_xen_swiotlb_init_late(void) { return -ENXIO; }
> -#endif
> -
>  int xen_swiotlb_fixup(void *buf, unsigned long nslabs);
>  int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
>  				unsigned int address_bits,
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index f887b08ac5ffe4..c4a7ead9eb674e 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -81,27 +81,6 @@ static void __init pci_xen_swiotlb_init(void)
>  	if (IS_ENABLED(CONFIG_PCI))
>  		pci_request_acs();
>  }
> -
> -int pci_xen_swiotlb_init_late(void)
> -{
> -	if (dma_ops == &xen_swiotlb_dma_ops)
> -		return 0;
> -
> -	/* we can work with the default swiotlb */
> -	if (!io_tlb_default_mem.nslabs) {
> -		int rc = swiotlb_init_late(swiotlb_size_or_default(),
> -					   GFP_KERNEL, xen_swiotlb_fixup);
> -		if (rc < 0)
> -			return rc;
> -	}
> -
> -	/* XXX: this switches the dma ops under live devices! */
> -	dma_ops = &xen_swiotlb_dma_ops;
> -	if (IS_ENABLED(CONFIG_PCI))
> -		pci_request_acs();
> -	return 0;
> -}
> -EXPORT_SYMBOL_GPL(pci_xen_swiotlb_init_late);
>  #else
>  static inline void __init pci_xen_swiotlb_init(void)
>  {
> @@ -111,7 +90,9 @@ static inline void __init pci_xen_swiotlb_init(void)
>  void __init pci_iommu_alloc(void)
>  {
>  	if (xen_pv_domain()) {
> -		if (xen_initial_domain() || x86_swiotlb_enable)
> +		if (xen_initial_domain() ||
> +		    IS_ENABLED(CONFIG_XEN_PCIDEV_FRONTEND) ||
> +		    x86_swiotlb_enable)
>  			pci_xen_swiotlb_init();
>  		return;
>  	}
> diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
> index 83c0ab50676dff..11636634ae512f 100644
> --- a/drivers/pci/xen-pcifront.c
> +++ b/drivers/pci/xen-pcifront.c
> @@ -22,7 +22,6 @@
>  #include <linux/bitops.h>
>  #include <linux/time.h>
>  #include <linux/ktime.h>
> -#include <linux/swiotlb.h>
>  #include <xen/platform_pci.h>
>  
>  #include <asm/xen/swiotlb-xen.h>
> @@ -669,11 +668,6 @@ static int pcifront_connect_and_init_dma(struct
pcifront_device *pdev)
>  
>  	spin_unlock(&pcifront_dev_lock);
>  
> -	if (!err && !is_swiotlb_active(&pdev->xdev->dev)) {
> -		err = pci_xen_swiotlb_init_late();
> -		if (err)
> -			dev_err(&pdev->xdev->dev, "Could not setup
SWIOTLB!\n");
> -	}
>  	return err;
>  }
>  
> -- 
> 2.39.2
> 
> 
-- 
Best Regards,
Marek Marczykowski-G?recki
Invisible Things Lab
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On Thu, May 18, 2023 at 08:18:39PM +0200, Marek Marczykowski-G?recki
wrote:
> On Thu, May 18, 2023 at 03:42:51PM +0200, Christoph Hellwig wrote:
> > Remove the dangerous late initialization of xen-swiotlb in
> > pci_xen_swiotlb_init_late and instead just always initialize
> > xen-swiotlb in the boot code if CONFIG_XEN_PCIDEV_FRONTEND is enabled.
> > 
> > Signed-off-by: Christoph Hellwig <hch at lst.de>
> 
> Doesn't it mean all the PV guests will basically waste 64MB of RAM
> by default each if they don't really have PCI devices?
If CONFIG_XEN_PCIDEV_FRONTEND is enabled, and the kernel's isn't booted
with swiotlb=noforce, yes.