kmsan: fix kmsan_handle_dma() to avoid false positives

KMSAN reports an uninitialized value issue in dma_map_phys()[1].  This
is a false positive caused by the way the virtual address is handled
in kmsan_handle_dma().  Fix it by translating the physical address to
a virtual address using phys_to_virt().

[1]
BUG: KMSAN: uninit-value in dma_map_phys+0xdc5/0x1060
 dma_map_phys+0xdc5/0x1060
 dma_map_page_attrs+0xcf/0x130
 e1000_xmit_frame+0x3c51/0x78f0
 dev_hard_start_xmit+0x22f/0xa30
 sch_direct_xmit+0x3b2/0xcf0
 __dev_queue_xmit+0x3588/0x5e60
 neigh_resolve_output+0x9c5/0xaf0
 ip6_finish_output2+0x24e0/0x2d30
 ip6_finish_output+0x903/0x10d0
 ip6_output+0x331/0x600
 mld_sendpack+0xb4a/0x1770
 mld_ifc_work+0x1328/0x19b0
 process_scheduled_works+0xb91/0x1d80
 worker_thread+0xedf/0x1590
 kthread+0xd5c/0xf00
 ret_from_fork+0x1f5/0x4c0
 ret_from_fork_asm+0x1a/0x30

Uninit was created at:
 __kmalloc_cache_noprof+0x8f5/0x16b0
 syslog_print+0x9a/0xef0
 do_syslog+0x849/0xfe0
 __x64_sys_syslog+0x97/0x100
 x64_sys_call+0x3cf8/0x3e30
 do_syscall_64+0xd9/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Bytes 0-89 of 90 are uninitialized
Memory access of size 90 starts at ffff8880367ed000

CPU: 1 UID: 0 PID: 1552 Comm: kworker/1:2 Not tainted 6.17.0-next-20250929 #26 PREEMPT(none)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-5.fc42 04/01/2014
Workqueue: mld mld_ifc_work

Fixes: 6eb1e76 ("kmsan: convert kmsan_handle_dma to use physical addresses")
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20251002051024.3096061-1-syoshida@redhat.com

Author: Shigeru Yoshida

mm/kmsan/hooks.c

@@ -339,13 +339,12 @@ static void kmsan_handle_dma_page(const void *addr, size_t size,
 void kmsan_handle_dma(phys_addr_t phys, size_t size,
 		      enum dma_data_direction dir)
 {
-	struct page *page = phys_to_page(phys);
 	u64 page_offset, to_go;
 	void *addr;
 
 	if (PhysHighMem(phys))
 		return;
-	addr = page_to_virt(page);
+	addr = phys_to_virt(phys);
 	/*
 	 * The kernel may occasionally give us adjacent DMA pages not belonging
 	 * to the same allocation. Process them separately to avoid triggering