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

Sasha Levin
2024-03-11T18:38:47Z

From: Michael Kelley <mhklinux@outlook.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@outlook.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Link: https://lore.kernel.org/r/20240116022008.1023398-2-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20240116022008.1023398-2-mhklinux@outlook.com>
Signed-off-by: Sasha Levin <sashal@kernel.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