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Subject: Re: [PATCH V1 3/6] xen/virtio: Add option to restrict memory access
 under Xen
To:     Stefano Stabellini <sstabellini@kernel.org>
Cc:     xen-devel@lists.xenproject.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Juergen Gross <jgross@suse.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Julien Grall <julien@xen.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Christoph Hellwig <hch@infradead.org>
References: <1650646263-22047-1-git-send-email-olekstysh@gmail.com>
 <1650646263-22047-4-git-send-email-olekstysh@gmail.com>
 <alpine.DEB.2.22.394.2204221526221.915916@ubuntu-linux-20-04-desktop>
From:   Oleksandr <olekstysh@gmail.com>
Message-ID: <3de2852b-0a94-fd1d-2eb6-fd818f33fc88@gmail.com>
Date:   Sat, 23 Apr 2022 10:05:22 +0300
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On 23.04.22 02:00, Stefano Stabellini wrote:

Hello Stefano


> On Fri, 22 Apr 2022, Oleksandr Tyshchenko wrote:
>> From: Juergen Gross <jgross@suse.com>
>>
>> Introduce Xen grant DMA-mapping layer which contains special DMA-mapping
>> routines for providing grant references as DMA addresses to be used by
>> frontends (e.g. virtio) in Xen guests.
>>
>> In order to support virtio in Xen guests add a config option XEN_VIRTIO
>> enabling the user to specify whether in all Xen guests virtio should
>> be able to access memory via Xen grant mappings only on the host side.
>>
>> As this also requires providing arch_has_restricted_virtio_memory_access
>> implementation, switch from a pure stub to a real function on Arm
>> and combine with existing implementation for the SEV guests on x86.
>>
>> Add the needed functionality by providing a special set of DMA ops
>> handling the needed grant operations for the I/O pages.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> There are a couple of minor things that checkpatch.pl reports,

Thank you for pointing this out, my fault.


>   but aside
> from those the patch looks fine to me.

good


The attached diff to be squashed for the new version. One thing remains:

checkpatch.pl says regarding drivers/xen/grant-dma-ops.c:

WARNING: added, moved or deleted file(s), does MAINTAINERS need updating?
#151:
new file mode 100644


Which, I assume, this is not an issue as new file falls under XEN 
HYPERVISOR INTERFACE maintainership?

scripts/get_maintainer.pl -f drivers/xen/grant-dma-ops.c
Boris Ostrovsky <boris.ostrovsky@oracle.com> (supporter:XEN HYPERVISOR 
INTERFACE)
Juergen Gross <jgross@suse.com> (supporter:XEN HYPERVISOR INTERFACE)
Stefano Stabellini <sstabellini@kernel.org> (reviewer:XEN HYPERVISOR 
INTERFACE)
xen-devel@lists.xenproject.org (moderated list:XEN HYPERVISOR INTERFACE)
linux-kernel@vger.kernel.org (open list)

[snip]

-- 
Regards,

Oleksandr Tyshchenko


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From 8d36fc5a3604a69848c300a42f1a78f8ace41829 Mon Sep 17 00:00:00 2001
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Date: Sat, 23 Apr 2022 09:23:04 +0300
Subject: [PATCH] fixup

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
---
 drivers/xen/Kconfig         |  2 ++
 drivers/xen/grant-dma-ops.c | 21 ++++++++++++---------
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index b95581f..1727337 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -350,4 +350,6 @@ config XEN_VIRTIO
 	  guest type this will require special support on the backend side
 	  (qemu or kernel, depending on the virtio device types used).
 
+	  If in doubt, say n.
+
 endmenu
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index 70d5d77..b9d93d7 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -139,7 +139,7 @@ static struct page *xen_grant_dma_alloc_pages(struct device *dev, size_t size,
 					      enum dma_data_direction dir,
 					      gfp_t gfp)
 {
-	WARN_ONCE(1, "xen_grant_dma_alloc_pages size %zu\n", size);
+	WARN_ONCE(1, "%s: size %zu\n", __func__, size);
 	return NULL;
 }
 
@@ -147,7 +147,7 @@ static void xen_grant_dma_free_pages(struct device *dev, size_t size,
 				     struct page *vaddr, dma_addr_t dma_handle,
 				     enum dma_data_direction dir)
 {
-	WARN_ONCE(1, "xen_grant_dma_free_pages size %zu\n", size);
+	WARN_ONCE(1, "%s: size %zu\n", __func__, size);
 }
 
 static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page,
@@ -160,7 +160,8 @@ static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page,
 	grant_ref_t grant;
 	dma_addr_t dma_handle;
 
-	BUG_ON(dir == DMA_NONE);
+	if (WARN_ON(dir == DMA_NONE))
+		return DMA_MAPPING_ERROR;
 
 	data = find_xen_grant_dma_data(dev);
 	if (!data)
@@ -190,7 +191,8 @@ static void xen_grant_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
 	unsigned int i, n_pages = PFN_UP(size);
 	grant_ref_t grant;
 
-	BUG_ON(dir == DMA_NONE);
+	if (WARN_ON(dir == DMA_NONE))
+		return;
 
 	data = find_xen_grant_dma_data(dev);
 	if (!data)
@@ -219,7 +221,8 @@ static void xen_grant_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
 	struct scatterlist *s;
 	unsigned int i;
 
-	BUG_ON(dir == DMA_NONE);
+	if (WARN_ON(dir == DMA_NONE))
+		return;
 
 	for_each_sg(sg, s, nents, i)
 		xen_grant_dma_unmap_page(dev, s->dma_address, sg_dma_len(s), dir,
@@ -233,7 +236,8 @@ static int xen_grant_dma_map_sg(struct device *dev, struct scatterlist *sg,
 	struct scatterlist *s;
 	unsigned int i;
 
-	BUG_ON(dir == DMA_NONE);
+	if (WARN_ON(dir == DMA_NONE))
+		return -EINVAL;
 
 	for_each_sg(sg, s, nents, i) {
 		s->dma_address = xen_grant_dma_map_page(dev, sg_page(s), s->offset,
@@ -303,10 +307,9 @@ void xen_grant_setup_dma_ops(struct device *dev)
 	}
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
-	if (!data) {
-		dev_err(dev, "Сannot allocate Xen grant DMA data\n");
+	if (!data)
 		goto err;
-	}
+
 	data->dev_domid = dev_domid;
 	data->dev = dev;
 
-- 
2.7.4


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