Re: [Cluster-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable

[Al Viro]

On Sat, Aug 28, 2021 at 10:19:04PM +0000, Al Viro wrote:

> How about taking __clear_user() out of copy_fpregs_to_sigframe()
> and replacing the call of fault_in_pages_writeable() with
>       if (!clear_user(buf_fx, fpu_user_xstate_size))
>               goto retry;
>       return -EFAULT;
> in the caller?

Something like this (completely untested)

Lift __clear_user() out of copy_fpregs_to_sigframe(), do not confuse EFAULT with
X86_TRAP_PF, don't bother with fault_in_pages_writeable() (pointless, since now
__clear_user() on error is not under pagefault_disable()).  And don't bother
with retries on anything other than #PF...

diff --git a/arch/x86/include/asm/fpu/internal.h 
b/arch/x86/include/asm/fpu/internal.h
index 5a18694a89b2..71c6621a262f 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -17,6 +17,7 @@
 #include <linux/mm.h>
 
 #include <asm/user.h>
+#include <asm/trapnr.h>
 #include <asm/fpu/api.h>
 #include <asm/fpu/xstate.h>
 #include <asm/fpu/xcr.h>
@@ -345,7 +346,7 @@ static inline int xsave_to_user_sigframe(struct xregs_state 
__user *buf)
         */
        err = __clear_user(&buf->header, sizeof(buf->header));
        if (unlikely(err))
-               return -EFAULT;
+               return -X86_TRAP_PF;
 
        stac();
        XSTATE_OP(XSAVE, buf, lmask, hmask, err);
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 445c57c9c539..611b9ed9c06b 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -135,18 +135,12 @@ static inline int save_xstate_epilog(void __user *buf, 
int ia32_frame)
 
 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
 {
-       int err;
-
        if (use_xsave())
-               err = xsave_to_user_sigframe(buf);
-       else if (use_fxsr())
-               err = fxsave_to_user_sigframe((struct fxregs_state __user *) 
buf);
+               return xsave_to_user_sigframe(buf);
+       if (use_fxsr())
+               return fxsave_to_user_sigframe((struct fxregs_state __user *) 
buf);
        else
-               err = fnsave_to_user_sigframe((struct fregs_state __user *) 
buf);
-
-       if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
-               err = -EFAULT;
-       return err;
+               return fnsave_to_user_sigframe((struct fregs_state __user *) 
buf);
 }
 
 /*
@@ -205,9 +199,10 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user 
*buf_fx, int size)
        fpregs_unlock();
 
        if (ret) {
-               if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
+               if (!__clear_user(buf_fx, fpu_user_xstate_size) &&
+                   ret == -X86_TRAP_PF)
                        goto retry;
-               return -EFAULT;
+               return -1;
        }
 
        /* Save the fsave header for the 32-bit frames. */
@@ -275,7 +270,7 @@ static int restore_fpregs_from_user(void __user *buf, u64 
xrestore,
                fpregs_unlock();
 
                /* Try to handle #PF, but anything else is fatal. */
-               if (ret != -EFAULT)
+               if (ret != -X86_TRAP_PF)
                        return -EINVAL;
 
                ret = fault_in_pages_readable(buf, size);