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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Xen-devel <xen-devel@lists.xenproject.org>
CC: Andrew Cooper <andrew.cooper3@citrix.com>, Jan Beulich
<JBeulich@suse.com>, =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?=
<roger.pau@citrix.com>, Wei Liu <wl@xen.org>, Jinoh Kang
<jinoh.kang.kr@gmail.com>
Subject: [PATCH 2/7] x86/emul: Fix and extend #DB trap handling
Date: Fri, 15 Sep 2023 21:36:23 +0100
Message-ID: <20230915203628.837732-3-andrew.cooper3@citrix.com>
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Lots of this is very very broken, but we need to start somewhere.
First, the bugfix. Hooks which use X86EMUL_DONE to skip the general emulat=
ion
still need to evaluate singlestep as part of completing the instruction.
Defer the logic until X86EMUL_DONE has been converted to X86EMUL_OKAY.
Second, the improvement. PENDING_DBG, INTERRUPTIBILITY and ACTIVITY are
internal pipeline state which Intel exposed to software in the VMCS, and AMD
exposed a subset of in the VMCB. Importantly, bits set in PENDING_DBG can
survive across multiple instruction boundaries if e.g. delivery of #DB is
delayed by a MovSS.
For now, introduce a full pending_dbg field into the retire union. This ke=
eps
the sh_page_fault() and init_context() paths working but in due course the
field will want to lose the "retire" infix.
In addition, set singlestep into pending_dbg as appropriate. Leave the old
singlestep bitfield in place until we can adjust the callers to the new
scheme.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monn=C3=A9 <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Jinoh Kang <jinoh.kang.kr@gmail.com>
v2:
* Only evaluate singlestep on X86EMUL_OKAY, but do so after X86EMUL_DONE h=
as
been adjusted to X86EMUL_OKAY.
* Adjust comments in light of X86EMUL_DONE not getting back to callers.
---
xen/arch/x86/x86_emulate/x86_emulate.c | 20 +++++++++++++-------
xen/arch/x86/x86_emulate/x86_emulate.h | 14 +++++++++++---
2 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emul=
ate/x86_emulate.c
index 94caec1d142c..de7f99500e3f 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -8379,13 +8379,6 @@ x86_emulate(
if ( !mode_64bit() )
_regs.r(ip) =3D (uint32_t)_regs.r(ip);
=20
- /* Should a singlestep #DB be raised? */
- if ( rc =3D=3D X86EMUL_OKAY && singlestep && !ctxt->retire.mov_ss )
- {
- ctxt->retire.singlestep =3D true;
- ctxt->retire.sti =3D false;
- }
-
if ( rc !=3D X86EMUL_DONE )
*ctxt->regs =3D _regs;
else
@@ -8394,6 +8387,19 @@ x86_emulate(
rc =3D X86EMUL_OKAY;
}
=20
+ /* Should a singlestep #DB be raised? */
+ if ( rc =3D=3D X86EMUL_OKAY && singlestep )
+ {
+ ctxt->retire.pending_dbg |=3D X86_DR6_BS;
+
+ /* BROKEN - TODO, merge into pending_dbg. */
+ if ( !ctxt->retire.mov_ss )
+ {
+ ctxt->retire.singlestep =3D true;
+ ctxt->retire.sti =3D false;
+ }
+ }
+
ctxt->regs->eflags &=3D ~X86_EFLAGS_RF;
=20
done:
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h b/xen/arch/x86/x86_emul=
ate/x86_emulate.h
index 698750267a90..fbc023c37e34 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -588,15 +588,23 @@ struct x86_emulate_ctxt
/* Canonical opcode (see below) (valid only on X86EMUL_OKAY). */
unsigned int opcode;
=20
- /* Retirement state, set by the emulator (valid only on X86EMUL_OKAY).=
*/
+ /*
+ * Retirement state, set by the emulator (valid only on X86EMUL_OKAY).
+ *
+ * TODO: all this state should be input/output from the VMCS PENDING_D=
BG,
+ * INTERRUPTIBILITY and ACTIVITIY fields.
+ */
union {
- uint8_t raw;
+ unsigned long raw;
struct {
+ /* Accumulated %dr6 trap bits, positive polarity. */
+ unsigned int pending_dbg;
+
bool hlt:1; /* Instruction HLTed. */
bool mov_ss:1; /* Instruction sets MOV-SS irq shadow. */
bool sti:1; /* Instruction sets STI irq shadow. */
bool unblock_nmi:1; /* Instruction clears NMI blocking. */
- bool singlestep:1; /* Singlestepping was active. */
+ bool singlestep:1; /* Singlestepping was active. (TODO, merg=
e into pending_dbg) */
};
} retire;
=20
--=20
2.30.2