linux-kernel - Re: [PATCH v2] PCI/P2PDMA: Allow P2PDMA on all AMD CPUs newer than the Zen family

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Date:   Thu, 30 Jul 2020 10:27:07 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alex Deucher <alexdeucher@...il.com>,
        Christian König <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>
Subject: Re: [PATCH v2] PCI/P2PDMA: Allow P2PDMA on all AMD CPUs newer than
 the Zen family

On Wed, Jul 29, 2020 at 05:18:44PM -0600, Logan Gunthorpe wrote:
> In order to avoid needing to add every new AMD CPU host bridge to the list
> every cycle, allow P2PDMA if the CPUs vendor is AMD and family is
> greater than 0x17 (Zen).
> 
> This should cut down a bunch of the churn adding to the list of allowed
> host bridges.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Alex Deucher <alexdeucher@...il.com>
> Cc: Christian König <christian.koenig@....com>
> Cc: Huang Rui <ray.huang@....com>

Thanks, applied as below with Alex's reviewed-by to pci/peer-to-peer
for v5.9.

I had to enable CONFIG_MEMORY_HOTREMOVE and CONFIG_ZONE_DEVICE in
order to compile p2pdma.c.  I see some reasons why that is, but it's
not exactly intuitive, especially for MEMORY_HOTREMOVE.


commit dea286bb71ba ("PCI/P2PDMA: Allow P2PDMA on AMD Zen and newer CPUs")
Author: Logan Gunthorpe <logang@...tatee.com>
Date:   Wed Jul 29 17:18:44 2020 -0600

    PCI/P2PDMA: Allow P2PDMA on AMD Zen and newer CPUs
    
    Allow P2PDMA if the CPU vendor is AMD and family is 0x17 (Zen) or greater.
    
    [bhelgaas: commit log, simplify #if/#else/#endif]
    Link: https://lore.kernel.org/r/20200729231844.4653-1-logang@deltatee.com
    Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
    Reviewed-by: Alex Deucher <alexander.deucher@....com>
    Cc: Christian König <christian.koenig@....com>
    Cc: Huang Rui <ray.huang@....com>

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index e8e444eeb1cd..1ec61fced4c3 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -273,6 +273,19 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
 	seq_buf_printf(buf, "%s;", pci_name(pdev));
 }
 
+static bool cpu_supports_p2pdma(void)
+{
+#ifdef CONFIG_X86
+	struct cpuinfo_x86 *c = &cpu_data(0);
+
+	/* Any AMD CPU whose family ID is Zen or newer supports p2pdma */
+	if (c->x86_vendor == X86_VENDOR_AMD && c->x86 >= 0x17)
+		return true;
+#endif
+
+	return false;
+}
+
 static const struct pci_p2pdma_whitelist_entry {
 	unsigned short vendor;
 	unsigned short device;
@@ -280,11 +293,6 @@ static const struct pci_p2pdma_whitelist_entry {
 		REQ_SAME_HOST_BRIDGE	= 1 << 0,
 	} flags;
 } pci_p2pdma_whitelist[] = {
-	/* AMD ZEN */
-	{PCI_VENDOR_ID_AMD,	0x1450,	0},
-	{PCI_VENDOR_ID_AMD,	0x15d0,	0},
-	{PCI_VENDOR_ID_AMD,	0x1630,	0},
-
 	/* Intel Xeon E5/Core i7 */
 	{PCI_VENDOR_ID_INTEL,	0x3c00, REQ_SAME_HOST_BRIDGE},
 	{PCI_VENDOR_ID_INTEL,	0x3c01, REQ_SAME_HOST_BRIDGE},
@@ -473,7 +481,8 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
 					      acs_redirects, acs_list);
 
 	if (map_type == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE) {
-		if (!host_bridge_whitelist(provider, client))
+		if (!cpu_supports_p2pdma() &&
+		    !host_bridge_whitelist(provider, client))
 			map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
 	}