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Subject[PATCH v4 21/22] x86/fpu/xstate: Support dynamic user state in the signal handling path
Date
Entering a signal handler, the kernel saves xstate in signal frame. The
dynamic user state is better to be saved only when used. fpu->state_mask
can help to exclude unused states.

Returning from a signal handler, XRSTOR re-initializes the excluded state
components.

Add a test case to verify in the signal handler that the signal frame
excludes AMX data when the signaled thread has initialized AMX state.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
---
Changes from v3:
* Removed 'no functional changes' in the changelog. (Borislav Petkov)

Changes from v1:
* Made it revertable (moved close to the end of the series).
* Included the test case.
---
arch/x86/include/asm/fpu/internal.h | 2 +-
tools/testing/selftests/x86/amx.c | 66 +++++++++++++++++++++++++++++
2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index c467312d38d8..090eb5bb277b 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -354,7 +354,7 @@ static inline void copy_kernel_to_xregs(struct xregs_state *xstate, u64 mask)
*/
static inline int copy_xregs_to_user(struct xregs_state __user *buf)
{
- u64 mask = xfeatures_mask_user();
+ u64 mask = current->thread.fpu.state_mask;
u32 lmask = mask;
u32 hmask = mask >> 32;
int err;
diff --git a/tools/testing/selftests/x86/amx.c b/tools/testing/selftests/x86/amx.c
index f4ecdfd27ae9..a7386b886532 100644
--- a/tools/testing/selftests/x86/amx.c
+++ b/tools/testing/selftests/x86/amx.c
@@ -650,6 +650,71 @@ static void test_ptrace(void)
test_tile_state_write(ptracee_loads_tiles);
}

+/* Signal handling test */
+
+static int sigtrapped;
+struct tile_data sig_tiles, sighdl_tiles;
+
+static void handle_sigtrap(int sig, siginfo_t *info, void *ctx_void)
+{
+ ucontext_t *uctxt = (ucontext_t *)ctx_void;
+ struct xsave_data xdata;
+ struct tile_config cfg;
+ struct tile_data tiles;
+ u64 header;
+
+ header = __get_xsave_xstate_bv((void *)uctxt->uc_mcontext.fpregs);
+
+ if (header & (1 << XFEATURE_XTILE_DATA))
+ printf("[FAIL]\ttile data was written in sigframe\n");
+ else
+ printf("[OK]\ttile data was skipped in sigframe\n");
+
+ set_tilecfg(&cfg);
+ load_tilecfg(&cfg);
+ init_xdata(&xdata);
+
+ make_tiles(&tiles);
+ copy_tiles_to_xdata(&xdata, &tiles);
+ restore_xdata(&xdata);
+
+ save_xdata(&xdata);
+ if (compare_xdata_tiles(&xdata, &tiles))
+ err(1, "tile load file");
+
+ printf("\tsignal handler: load tile data\n");
+
+ sigtrapped = sig;
+}
+
+static void test_signal_handling(void)
+{
+ struct xsave_data xdata = { 0 };
+ struct tile_data tiles = { 0 };
+
+ sethandler(SIGTRAP, handle_sigtrap, 0);
+ sigtrapped = 0;
+
+ printf("[RUN]\tCheck tile state management in handling signal\n");
+
+ printf("\tbefore signal: initial tile data state\n");
+
+ raise(SIGTRAP);
+
+ if (sigtrapped == 0)
+ err(1, "sigtrap");
+
+ save_xdata(&xdata);
+ if (compare_xdata_tiles(&xdata, &tiles)) {
+ printf("[FAIL]\ttile data was not loaded at sigreturn\n");
+ nerrs++;
+ } else {
+ printf("[OK]\ttile data was re-initialized at sigreturn\n");
+ }
+
+ clearhandler(SIGTRAP);
+}
+
int main(void)
{
/* Check hardware availability at first */
@@ -672,6 +737,7 @@ int main(void)
test_fork();
test_context_switch();
test_ptrace();
+ test_signal_handling();

return nerrs ? 1 : 0;
}
--
2.17.1
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