linux-kernel - [PATCH AUTOSEL 6.1 3/7] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback

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Message-ID: <20240311183826.328535-3-sashal@kernel.org>
Date: Mon, 11 Mar 2024 14:38:21 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Michael Kelley <mhklinux@...look.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Wei Liu <wei.liu@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	kys@...rosoft.com,
	haiyangz@...rosoft.com,
	sthemmin@...rosoft.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	x86@...nel.org,
	dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	devel@...uxdriverproject.org
Subject: [PATCH AUTOSEL 6.1 3/7] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback

From: Michael Kelley <mhklinux@...look.com>

[ Upstream commit 9fef276f9f416a1e85eb48d3bd38e6018a220bf5 ]

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@...look.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Link: https://lore.kernel.org/r/20240116022008.1023398-2-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@...nel.org>
Message-ID: <20240116022008.1023398-2-mhklinux@...look.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 1dbcbd9da74d4..fd08270dd7946 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -332,6 +332,8 @@ int hv_set_mem_host_visibility(unsigned long kbuffer, int pagecount, bool visibl
 	enum hv_mem_host_visibility visibility = visible ?
 			VMBUS_PAGE_VISIBLE_READ_WRITE : VMBUS_PAGE_NOT_VISIBLE;
 	u64 *pfn_array;
+	phys_addr_t paddr;
+	void *vaddr;
 	int ret = 0;
 	int i, pfn;
 
@@ -343,7 +345,15 @@ int hv_set_mem_host_visibility(unsigned long kbuffer, int pagecount, bool visibl
 		return -ENOMEM;
 
 	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 5f0ce77a259d8..fcc0d0f16be3f 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -723,10 +723,14 @@ 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)
 {
-- 
2.43.0