linux-kernel - [PATCH v2 4/4] swiotlb-xen: this is PV-only on x86

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Message-ID: <5947b8ae-fdc7-225c-4838-84712265fc1e@suse.com>
Date:   Fri, 17 Sep 2021 12:50:38 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "hch@....de" <hch@....de>, Konrad Wilk <konrad.wilk@...cle.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Subject: [PATCH v2 4/4] swiotlb-xen: this is PV-only on x86

The code is unreachable for HVM or PVH, and it also makes little sense
in auto-translated environments. On Arm, with
xen_{create,destroy}_contiguous_region() both being stubs, I have a hard
time seeing what good the Xen specific variant does - the generic one
ought to be fine for all purposes there. Still Arm code explicitly
references symbols here, so the code will continue to be included there.

Instead of making PCI_XEN's "select" conditional, simply drop it -
SWIOTLB_XEN will be available unconditionally in the PV case anyway, and
is - as explained above - dead code in non-PV environments.

This in turn allows dropping the stubs for
xen_{create,destroy}_contiguous_region(), the former of which was broken
anyway - it failed to set the DMA handle output.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2605,7 +2605,6 @@ config PCI_OLPC
 config PCI_XEN
 	def_bool y
 	depends on PCI && XEN
-	select SWIOTLB_XEN
 
 config MMCONF_FAM10H
 	def_bool y
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -177,6 +177,7 @@ config XEN_GRANT_DMA_ALLOC
 
 config SWIOTLB_XEN
 	def_bool y
+	depends on XEN_PV || ARM || ARM64
 	select DMA_OPS
 	select SWIOTLB
 
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -46,19 +46,7 @@ extern unsigned long *xen_contiguous_bit
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
 				unsigned int address_bits,
 				dma_addr_t *dma_handle);
-
 void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order);
-#else
-static inline int xen_create_contiguous_region(phys_addr_t pstart,
-					       unsigned int order,
-					       unsigned int address_bits,
-					       dma_addr_t *dma_handle)
-{
-	return 0;
-}
-
-static inline void xen_destroy_contiguous_region(phys_addr_t pstart,
-						 unsigned int order) { }
 #endif
 
 #if defined(CONFIG_XEN_PV)