On 12/5/18 8:36 AM, Sean Christopherson wrote:
> ...instead of manually handling the case where error_code=0, e.g. to
> display "[SUPERVISOR] [READ]" instead of "normal kernel read fault".
>
> This makes the zero case consistent with all other messages and also
> provides additional information for other error code combinations,
> e.g. error_code==1 will display "[PROT] [SUPERVISOR] [READ]" instead
> of simply "[PROT]".
>
> Print unique names for the negative cases as opposed to e.g. "[!USER]"
> to avoid mixups due to users missing a single "!" character, and to be
> more concise for the !INSTR && !WRITE case.
>
> Print "SUPERVISOR" in favor of "KERNEL" to reduce the likelihood that
> the message is misinterpreted as a generic kernel/software error and
> to be consistent with the SDM's nomenclature.
>
> An alternative to passing a negated error code to err_str_append() would
> be to expand err_str_append() to take a second string for the negative
> test, but that approach complicates handling the "[READ]" case, which
> looks for !INSTR && !WRITE, e.g. it would require an extra call to
> err_str_append() and logic in err_str_append() to allow null messages
> for both the positive and negative tests. Printing "[INSTR] [READ]"
> wouldn't be the end of the world, but a little bit of trickery in the
> kernel is a relatively small price to pay in exchange for the ability
> to unequivocally know the access type by reading a single word.
>
> Now that all components of the message use the [<code>] format,
> explicitly state that it's the error *code* that's being printed and
> group the err_str_append() calls by type so that the resulting print
> messages are consistent, e.g. the deciphered codes will always be:
>
> [PROT] [USER|SUPERVISOR] [WRITE|INSTR|READ] [RSDV] [PK]
RSVD
but it's correct in the patch.
BTW, what does PK mean?
thanks.
>
> Cc: Andy Lutomirski <l...@kernel.org>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: Dave Hansen <dave.han...@linux.intel.com>
> Cc: H. Peter Anvin <h...@zytor.com>
> Cc: Linus Torvalds <torva...@linux-foundation.org>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Rik van Riel <r...@surriel.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Yu-cheng Yu <yu-cheng...@intel.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: Ingo Molnar <mi...@kernel.org>
> Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
> ---
> arch/x86/mm/fault.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 2ff25ad33233..0b4ce5d2b461 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -609,7 +609,7 @@ static void show_ldttss(const struct desc_ptr *gdt, const
> char *name, u16 index)
> */
> static void err_str_append(unsigned long error_code, char *buf, unsigned
> long mask, const char *txt)
> {
> - if (error_code & mask) {
> + if ((error_code & mask) == mask) {
> if (buf[0])
> strcat(buf, " ");
> strcat(buf, txt);
> @@ -655,13 +655,16 @@ show_fault_oops(struct pt_regs *regs, unsigned long
> error_code, unsigned long ad
> * zero delimiter must fit into err_txt[].
> */
> err_str_append(error_code, err_txt, X86_PF_PROT, "[PROT]" );
> - err_str_append(error_code, err_txt, X86_PF_WRITE, "[WRITE]");
> err_str_append(error_code, err_txt, X86_PF_USER, "[USER]" );
> - err_str_append(error_code, err_txt, X86_PF_RSVD, "[RSVD]" );
> + err_str_append(~error_code, err_txt, X86_PF_USER, "[SUPERVISOR]");
> + err_str_append(error_code, err_txt, X86_PF_WRITE, "[WRITE]");
> err_str_append(error_code, err_txt, X86_PF_INSTR, "[INSTR]");
> + err_str_append(~error_code, err_txt, X86_PF_WRITE | X86_PF_INSTR,
> + "[READ]");
> + err_str_append(error_code, err_txt, X86_PF_RSVD, "[RSVD]" );
> err_str_append(error_code, err_txt, X86_PF_PK, "[PK]" );
>
> - pr_alert("#PF error: %s\n", error_code ? err_txt : "[normal kernel read
> fault]");
> + pr_alert("#PF error code: %s\n", err_txt);
>
> if (!(error_code & X86_PF_USER) && user_mode(regs)) {
> struct desc_ptr idt, gdt;
>
--
~Randy
