Received-SPF: pass (google.com: domain of linux-kernel+bounces-26927-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
From: mhkelley58@gmail.com
To: tglx@linutronix.de,
	mingo@redhat.com,
	bp@alien8.de,
	dave.hansen@linux.intel.com,
	x86@kernel.org,
	hpa@zytor.com,
	kirill.shutemov@linux.intel.com,
	haiyangz@microsoft.com,
	wei.liu@kernel.org,
	decui@microsoft.com,
	luto@kernel.org,
	peterz@infradead.org,
	akpm@linux-foundation.org,
	urezki@gmail.com,
	hch@infradead.org,
	lstoakes@gmail.com,
	thomas.lendacky@amd.com,
	ardb@kernel.org,
	jroedel@suse.de,
	seanjc@google.com,
	rick.p.edgecombe@intel.com,
	sathyanarayanan.kuppuswamy@linux.intel.com,
	linux-kernel@vger.kernel.org,
	linux-coco@lists.linux.dev,
	linux-hyperv@vger.kernel.org,
	linux-mm@kvack.org
Subject: [PATCH v4 1/3] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback
Date: Mon, 15 Jan 2024 18:20:06 -0800
Message-Id: <20240116022008.1023398-2-mhklinux@outlook.com>
In-Reply-To: <20240116022008.1023398-1-mhklinux@outlook.com>
References: <20240116022008.1023398-1-mhklinux@outlook.com>
Reply-To: mhklinux@outlook.com
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

From: Michael Kelley <mhklinux@outlook.com>

In preparation for temporarily marking pages not present during a
transition between encrypted and decrypted, use slow_virt_to_phys()
in the hypervisor callback. As long as the PFN is correct,
slow_virt_to_phys() works even if the leaf PTE is not present.
The existing functions that depend on vmalloc_to_page() all
require that the leaf PTE be marked present, so they don't work.

Update the comments for slow_virt_to_phys() to note this broader usage
and the requirement to work even if the PTE is not marked present.

Signed-off-by: Michael Kelley <mhklinux@outlook.com>
---
 arch/x86/hyperv/ivm.c        | 12 +++++++++++-
 arch/x86/mm/pat/set_memory.c | 12 ++++++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 02e55237d919..851107c77f4d 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -515,6 +515,8 @@ static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bo
 	enum hv_mem_host_visibility visibility = enc ?
 			VMBUS_PAGE_NOT_VISIBLE : VMBUS_PAGE_VISIBLE_READ_WRITE;
 	u64 *pfn_array;
+	phys_addr_t paddr;
+	void *vaddr;
 	int ret = 0;
 	bool result = true;
 	int i, pfn;
@@ -524,7 +526,15 @@ static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bo
 		return false;
 
 	for (i = 0, pfn = 0; i < pagecount; i++) {
-		pfn_array[pfn] = virt_to_hvpfn((void *)kbuffer + i * HV_HYP_PAGE_SIZE);
+		/*
+		 * Use slow_virt_to_phys() because the PRESENT bit has been
+		 * temporarily cleared in the PTEs.  slow_virt_to_phys() works
+		 * without the PRESENT bit while virt_to_hvpfn() or similar
+		 * does not.
+		 */
+		vaddr = (void *)kbuffer + (i * HV_HYP_PAGE_SIZE);
+		paddr = slow_virt_to_phys(vaddr);
+		pfn_array[pfn] = paddr >> HV_HYP_PAGE_SHIFT;
 		pfn++;
 
 		if (pfn == HV_MAX_MODIFY_GPA_REP_COUNT || i == pagecount - 1) {
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index bda9f129835e..e76ac64b516e 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -755,10 +755,14 @@ pmd_t *lookup_pmd_address(unsigned long address)
  * areas on 32-bit NUMA systems.  The percpu areas can
  * end up in this kind of memory, for instance.
  *
- * This could be optimized, but it is only intended to be
- * used at initialization time, and keeping it
- * unoptimized should increase the testing coverage for
- * the more obscure platforms.
+ * Note that as long as the PTEs are well-formed with correct PFNs, this
+ * works without checking the PRESENT bit in the leaf PTE.  This is unlike
+ * the similar vmalloc_to_page() and derivatives.  Callers may depend on
+ * this behavior.
+ *
+ * This could be optimized, but it is only used in paths that are not perf
+ * sensitive, and keeping it unoptimized should increase the testing coverage
+ * for the more obscure platforms.
  */
 phys_addr_t slow_virt_to_phys(void *__virt_addr)
 {
-- 
2.25.1