linux-kernel - [RFC PATCH 07/11] powerpc/svm: Use shared memory for Debug Trace Log (DTL)

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Date:   Thu, 23 Aug 2018 23:59:29 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Ram Pai <linuxram@...ibm.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Subject: [RFC PATCH 07/11] powerpc/svm: Use shared memory for Debug Trace Log (DTL)

From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>

On Ultravisor platform kmem_cache for DTL buffers must use a constructor
function which converts the underlying buddy allocated SLUB cache pages
into shared memory so that they are accessible to the hypervisor.

Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
---
 arch/powerpc/include/asm/svm.h         |  1 +
 arch/powerpc/kernel/svm.c              | 30 ++++++++++++++++++++++++++++++
 arch/powerpc/platforms/pseries/setup.c |  5 ++++-
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/svm.h b/arch/powerpc/include/asm/svm.h
index 95d69e472e52..e00688761704 100644
--- a/arch/powerpc/include/asm/svm.h
+++ b/arch/powerpc/include/asm/svm.h
@@ -16,6 +16,7 @@ static bool is_svm_platform(void)
 
 extern void mem_convert_shared(unsigned long pfn, unsigned long npages);
 extern void mem_convert_secure(unsigned long pfn, unsigned long npages);
+extern void dtl_cache_ctor(void *addr);
 #else
 static inline bool is_svm_platform(void)
 {
diff --git a/arch/powerpc/kernel/svm.c b/arch/powerpc/kernel/svm.c
index 891db2de8c04..1af5caa955f5 100644
--- a/arch/powerpc/kernel/svm.c
+++ b/arch/powerpc/kernel/svm.c
@@ -66,3 +66,33 @@ int set_memory_decrypted(unsigned long addr, int numpages)
 
 	return 0;
 }
+
+/* There's one dispatch log per CPU. */
+#define NR_DTL_PAGE (DISPATCH_LOG_BYTES * CONFIG_NR_CPUS / PAGE_SIZE)
+
+static struct page *dtl_page_store[NR_DTL_PAGE];
+static long dtl_nr_pages;
+
+static bool is_dtl_page_shared(struct page *page)
+{
+	long i;
+
+	for (i = 0; i < dtl_nr_pages; i++)
+		if (dtl_page_store[i] == page)
+			return true;
+
+	return false;
+}
+
+void dtl_cache_ctor(void *addr)
+{
+	unsigned long pfn = PHYS_PFN(__pa(addr));
+	struct page *page = pfn_to_page(pfn);
+
+	if (!is_dtl_page_shared(page)) {
+		dtl_page_store[dtl_nr_pages] = page;
+		dtl_nr_pages++;
+		WARN_ON(dtl_nr_pages >= NR_DTL_PAGE);
+		mem_convert_shared(pfn, PAGE_SIZE);
+	}
+}
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 139f0af6c3d9..50ba77c802d2 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -69,6 +69,7 @@
 #include <asm/kexec.h>
 #include <asm/isa-bridge.h>
 #include <asm/security_features.h>
+#include <asm/svm.h>
 
 #include "pseries.h"
 
@@ -288,8 +289,10 @@ static inline int alloc_dispatch_logs(void)
 
 static int alloc_dispatch_log_kmem_cache(void)
 {
+	void (*ctor)(void *) = is_svm_platform() ? dtl_cache_ctor : NULL;
+
 	dtl_cache = kmem_cache_create("dtl", DISPATCH_LOG_BYTES,
-						DISPATCH_LOG_BYTES, 0, NULL);
+						DISPATCH_LOG_BYTES, 0, ctor);
 	if (!dtl_cache) {
 		pr_warn("Failed to create dispatch trace log buffer cache\n");
 		pr_warn("Stolen time statistics will be unreliable\n");