Re: [PATCHv8 13/17] x86/traps: Generalize #GP address decode and hint code

Sohil Mehta
2025-07-02T00:55:23Z

On 7/1/2025 2:58 AM, Kirill A. Shutemov wrote:
> Handlers for #GP and #SS will now share code to decode the exception
> address and retrieve the exception hint string.
>

This is missing an essential "why"? Why do #GP and #SS handlers need to
share code? None of the patches prior to this have hinted this.

It can probably be deduced from a later patch, but it needs to be
clarified in this one. Maybe a simplified version of the text from the SDM:

"In most cases, an access causing a LASS violation results in a general
protection exception (#GP); for stack accesses (those due to
stack-oriented instructions, as well as accesses that implicitly or
explicitly use the SS segment register), a stack fault (#SS) is generated."

> The helper, enum, and array should be renamed as they are no longer
> specific to #GP.
>
> No functional change intended.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> arch/x86/kernel/traps.c | 62 ++++++++++++++++++++---------------------
> 1 file changed, 31 insertions(+), 31 deletions(-)
>

The code changes look okay to me except a minor nit below.

> #define GPFSTR "general protection fault"
> @@ -808,8 +808,8 @@ static void gp_user_force_sig_segv(struct pt_regs *regs, int trapnr,
> DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
> {
> char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
> - enum kernel_gp_hint hint = GP_NO_HINT;
> - unsigned long gp_addr;

gp_addr is a local variable to the #GP handler. It can probably stay the
same.

> + enum kernel_exc_hint hint = EXC_NO_HINT;
> + unsigned long exc_addr;
>
> if (user_mode(regs) && try_fixup_enqcmd_gp())
> return;
> @@ -846,21 +846,21 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
> if (error_code)
> snprintf(desc, sizeof(desc), "segment-related " GPFSTR);
> else
> - hint = get_kernel_gp_address(regs, &gp_addr);
> + hint = get_kernel_exc_address(regs, &exc_addr);
>
> - if (hint != GP_NO_HINT) {
> + if (hint != EXC_NO_HINT) {
> snprintf(desc, sizeof(desc), GPFSTR ", %s 0x%lx",
> - kernel_gp_hint_help[hint], gp_addr);
> + kernel_exc_hint_help[hint], exc_addr);
> }
>
> /*
> * KASAN is interested only in the non-canonical case, clear it
> * otherwise.
> */
> - if (hint != GP_NON_CANONICAL)
> - gp_addr = 0;
> + if (hint != EXC_NON_CANONICAL)
> + exc_addr = 0;
>
> - die_addr(desc, regs, error_code, gp_addr);
> + die_addr(desc, regs, error_code, exc_addr);
>
> exit:
> cond_local_irq_disable(regs);