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

[Juergen Gross <jgross@suse.com>]

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On 09.06.23 17:38, Juergen Gross wrote:
> On 07.06.23 15:12, Christoph Hellwig wrote:
>> On Mon, May 22, 2023 at 10:37:09AM +0200, Juergen Gross wrote:
>>> In normal cases PCI passthrough in PV guests requires to start the guest
>>> with e820_host=1. So it should be rather easy to limit allocating the
>>> 64MB in PV guests to the cases where the memory map has non-RAM regions
>>> especially in the first 1MB of the memory.
>>>
>>> This will cover even hotplug cases. The only case not covered would be a
>>> guest started with e820_host=1 even if no PCI passthrough was planned.
>>> But this should be rather rare (at least I hope so).
>>
>> So is this an ACK for the patch and can we go ahead with it?
> 
> As long as above mentioned check of the E820 map is done, yes.
> 
> If you want I can send a diff to be folded into your patch on Monday.

Attached is a patch for adding a new flag xen_pv_pci_possible. You can
either add the patch to your series or merge it into your patch 2.

You need to modify your patch like this:

@@ -111,7 +90,10 @@ 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) &&
+		     xen_pv_pci_possible) ||
+		    x86_swiotlb_enable)
  			pci_xen_swiotlb_init();
  		return;
  	}


Juergen

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From 7e84a88243b57bc90d1ef6bd42661f499886e659 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Mon, 12 Jun 2023 09:57:18 +0200
Subject: [PATCH] xen/pci: add flag for PCI passthrough being possible

When running as a Xen PV guests passed through PCI devices only have a
chance to work if the Xen supplied memory map has some PCI space
reserved.

Add a flag xen_pv_pci_possible which will be set in early boot in case
the memory map has at least one area with the type E820_TYPE_RESERVED.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/xen/setup.c | 6 ++++++
 include/xen/xen.h    | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index c2be3efb2ba0..716f76c41416 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -43,6 +43,9 @@ struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
 /* Number of pages released from the initial allocation. */
 unsigned long xen_released_pages;
 
+/* Memory map would allow PCI passthrough. */
+bool xen_pv_pci_possible;
+
 /* E820 map used during setting up memory. */
 static struct e820_table xen_e820_table __initdata;
 
@@ -804,6 +807,9 @@ char * __init xen_memory_setup(void)
 		chunk_size = size;
 		type = xen_e820_table.entries[i].type;
 
+		if (type == E820_TYPE_RESERVED)
+			xen_pv_pci_possible = true;
+
 		if (type == E820_TYPE_RAM) {
 			if (addr < mem_end) {
 				chunk_size = min(size, mem_end - addr);
diff --git a/include/xen/xen.h b/include/xen/xen.h
index 0efeb652f9b8..5eb0a974a11e 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -29,6 +29,12 @@ extern bool xen_pvh;
 
 extern uint32_t xen_start_flags;
 
+#ifdef CONFIG_XEN_PV
+extern bool xen_pv_pci_possible;
+#else
+#define xen_pv_pci_possible	0
+#endif
+
 #include <xen/interface/hvm/start_info.h>
 extern struct hvm_start_info pvh_start_info;
 
-- 
2.35.3


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