On 29.06.23 16:40, Jiri Slaby wrote:

On 27. 02. 23, 18:36, Suren Baghdasaryan wrote:

quoted

Attempt VMA lock-based page fault handling first, and fall back to the
existing mmap_lock-based handling if that fails.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
  arch/x86/Kconfig    |  1 +
  arch/x86/mm/fault.c | 36 ++++++++++++++++++++++++++++++++++++
  2 files changed, 37 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a825bf031f49..df21fba77db1 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -27,6 +27,7 @@ config X86_64

      # Options that are inherently 64-bit kernel only:
      select ARCH_HAS_GIGANTIC_PAGE
      select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
+    select ARCH_SUPPORTS_PER_VMA_LOCK
      select ARCH_USE_CMPXCHG_LOCKREF
      select HAVE_ARCH_SOFT_DIRTY
      select MODULES_USE_ELF_RELA

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index a498ae1fbe66..e4399983c50c 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c

@@ -19,6 +19,7 @@

  #include <linux/uaccess.h>        /* faulthandler_disabled()    */
  #include <linux/efi.h>            /*
efi_crash_gracefully_on_page_fault()*/
  #include <linux/mm_types.h>
+#include <linux/mm.h>            /* find_and_lock_vma() */
    #include <asm/cpufeature.h>        /* boot_cpu_has, ...        */
  #include <asm/traps.h>            /* dotraplinkage, ...        */

@@ -1333,6 +1334,38 @@ void do_user_addr_fault(struct pt_regs *regs,

      }
  #endif
  +#ifdef CONFIG_PER_VMA_LOCK
+    if (!(flags & FAULT_FLAG_USER))
+        goto lock_mmap;
+
+    vma = lock_vma_under_rcu(mm, address);
+    if (!vma)
+        goto lock_mmap;
+
+    if (unlikely(access_error(error_code, vma))) {
+        vma_end_read(vma);
+        goto lock_mmap;
+    }
+    fault = handle_mm_fault(vma, address, flags |
FAULT_FLAG_VMA_LOCK, regs);
+    vma_end_read(vma);
+
+    if (!(fault & VM_FAULT_RETRY)) {
+        count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+        goto done;
+    }
+    count_vm_vma_lock_event(VMA_LOCK_RETRY);

This is apparently not strong enough as it causes go build failures like:

TWIMC & for the record: there is another report about trouble caused by
this change; for details see

https://bugzilla.kernel.org/show_bug.cgi?id=217624

And a "forward to devs and lists" thread about that report:

https://lore.kernel.org/all/facbfec3-837a-51ed-85fa-31021c17d6ef@gmail.com/ (local)

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

[  409s] strconv
[  409s] releasep: m=0x579e2000 m->p=0x5781c600 p->m=0x0 p->status=2
[  409s] fatal error: releasep: invalid p state
[  409s]

[  325s] hash/adler32
[  325s] hash/crc32
[  325s] cmd/internal/codesign
[  336s] fatal error: runtime: out of memory

There are many kinds of similar errors. It happens in 1-3 out of 20
builds only.

If I revert the commit on top of 6.4, they all dismiss. Any idea?

The downstream report:
https://bugzilla.suse.com/show_bug.cgi?id=1212775

quoted

+
+    /* Quick path to respond to signals */
+    if (fault_signal_pending(fault, regs)) {
+        if (!user_mode(regs))
+            kernelmode_fixup_or_oops(regs, error_code, address,
+                         SIGBUS, BUS_ADRERR,
+                         ARCH_DEFAULT_PKEY);
+        return;
+    }
+lock_mmap:
+#endif /* CONFIG_PER_VMA_LOCK */
+
      /*
       * Kernel-mode access to the user address space should only occur
       * on well-defined single instructions listed in the exception

@@ -1433,6 +1466,9 @@ void do_user_addr_fault(struct pt_regs *regs,

      }
        mmap_read_unlock(mm);
+#ifdef CONFIG_PER_VMA_LOCK
+done:
+#endif
      if (likely(!(fault & VM_FAULT_ERROR)))
          return;
  

thanks,