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([172.25.112.68]) by fmsmga006.fm.intel.com with ESMTP; 01 Mar 2023 21:50:49 -0800 From: Xin Li To: linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org, andrew.cooper3@citrix.com, seanjc@google.com, pbonzini@redhat.com, ravi.v.shankar@intel.com Subject: [PATCH v4 18/34] x86/fred: add a debug fault entry stub for FRED Date: Wed, 1 Mar 2023 21:24:55 -0800 Message-Id: <20230302052511.1918-19-xin3.li@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230302052511.1918-1-xin3.li@intel.com> References: <20230302052511.1918-1-xin3.li@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: "H. Peter Anvin (Intel)" Add a debug fault entry stub for FRED. On a FRED system, the debug trap status information (DR6) is passed on the stack, to avoid the problem of transient state. Furthermore, FRED transitions avoid a lot of ugly corner cases the handling of which can, and should be, skipped. The FRED debug trap status information saved on the stack differs from DR6 in both stickiness and polarity; it is exactly what debug_read_clear_dr6() returns, and exc_debug_user()/exc_debug_kernel() expect. Signed-off-by: H. Peter Anvin (Intel) Tested-by: Shan Kang Signed-off-by: Xin Li --- Changes since v1: * call irqentry_nmi_{enter,exit}() in both IDT and FRED debug fault kernel handler (Peter Zijlstra). --- arch/x86/include/asm/fred.h | 1 + arch/x86/kernel/traps.c | 56 +++++++++++++++++++++++++++---------- 2 files changed, 42 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h index 57affbf80ced..633dd9e6a68e 100644 --- a/arch/x86/include/asm/fred.h +++ b/arch/x86/include/asm/fred.h @@ -94,6 +94,7 @@ static __always_inline unsigned long fred_event_data(stru= ct pt_regs *regs) #define DEFINE_FRED_HANDLER(f) noinstr DECLARE_FRED_HANDLER(f) typedef DECLARE_FRED_HANDLER((*fred_handler)); =20 +DECLARE_FRED_HANDLER(fred_exc_debug); DECLARE_FRED_HANDLER(fred_exc_page_fault); =20 #endif /* __ASSEMBLY__ */ diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index cebba1f49e19..4b0f63344526 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -47,6 +47,7 @@ #include #include #include +#include #include #include #include @@ -1020,21 +1021,9 @@ static bool notify_debug(struct pt_regs *regs, unsig= ned long *dr6) return false; } =20 -static __always_inline void exc_debug_kernel(struct pt_regs *regs, - unsigned long dr6) +static __always_inline void debug_kernel_common(struct pt_regs *regs, + unsigned long dr6) { - /* - * Disable breakpoints during exception handling; recursive exceptions - * are exceedingly 'fun'. - * - * Since this function is NOKPROBE, and that also applies to - * HW_BREAKPOINT_X, we can't hit a breakpoint before this (XXX except a - * HW_BREAKPOINT_W on our stack) - * - * Entry text is excluded for HW_BP_X and cpu_entry_area, which - * includes the entry stack is excluded for everything. - */ - unsigned long dr7 =3D local_db_save(); irqentry_state_t irq_state =3D irqentry_nmi_enter(regs); instrumentation_begin(); =20 @@ -1062,7 +1051,8 @@ static __always_inline void exc_debug_kernel(struct p= t_regs *regs, * Catch SYSENTER with TF set and clear DR_STEP. If this hit a * watchpoint at the same time then that will still be handled. */ - if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs)) + if (!cpu_feature_enabled(X86_FEATURE_FRED) && + (dr6 & DR_STEP) && is_sysenter_singlestep(regs)) dr6 &=3D ~DR_STEP; =20 /* @@ -1090,7 +1080,25 @@ static __always_inline void exc_debug_kernel(struct = pt_regs *regs, out: instrumentation_end(); irqentry_nmi_exit(regs, irq_state); +} =20 +static __always_inline void exc_debug_kernel(struct pt_regs *regs, + unsigned long dr6) +{ + /* + * Disable breakpoints during exception handling; recursive exceptions + * are exceedingly 'fun'. + * + * Since this function is NOKPROBE, and that also applies to + * HW_BREAKPOINT_X, we can't hit a breakpoint before this (XXX except a + * HW_BREAKPOINT_W on our stack) + * + * Entry text is excluded for HW_BP_X and cpu_entry_area, which + * includes the entry stack is excluded for everything. + */ + unsigned long dr7 =3D local_db_save(); + + debug_kernel_common(regs, dr6); local_db_restore(dr7); } =20 @@ -1179,6 +1187,24 @@ DEFINE_IDTENTRY_DEBUG_USER(exc_debug) { exc_debug_user(regs, debug_read_clear_dr6()); } + +# ifdef CONFIG_X86_FRED +DEFINE_FRED_HANDLER(fred_exc_debug) +{ + /* + * The FRED debug information saved onto stack differs from + * DR6 in both stickiness and polarity; it is exactly what + * debug_read_clear_dr6() returns. + */ + unsigned long dr6 =3D fred_event_data(regs); + + if (user_mode(regs)) + exc_debug_user(regs, dr6); + else + debug_kernel_common(regs, dr6); +} +# endif /* CONFIG_X86_FRED */ + #else /* 32 bit does not have separate entry points. */ DEFINE_IDTENTRY_RAW(exc_debug) --=20 2.34.1