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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Sean Christopherson" <sean.j.christopherson@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Arnd Bergmann" <arnd@arndb.de>, "Jann Horn" <jannh@google.com>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH v2 04/22] x86/kvm: Don't call kvm_spurious_fault() from .fixup
Date: Thu, 18 Jul 2019 09:12:10 -0500	[thread overview]
Message-ID: <20190718141210.us7giumvgbgifvtv@treble> (raw)
In-Reply-To: <1b891612-18e6-48ed-cfb5-05e8aca79dcb@redhat.com>

On Thu, Jul 18, 2019 at 03:18:50PM +0200, Paolo Bonzini wrote:
> On 18/07/19 15:16, Sean Christopherson wrote:
> >> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> >>
> >> This has a side effect of adding a jump in a generally hot path, but
> >> let's hope that the speculation gods for once help us.
> > Any reason not to take the same approach as vmx_vmenter() and ud2 directly
> > from fixup?  I've never found kvm_spurious_fault() to be all that helpful,
> > IMO it's a win win. :-)
> 
> Honestly I've never seen a backtrace from here but I would rather not
> regret this when a customer encounters it...

In theory, changing the "call kvm_spurious_fault" to ud2 should be fine.
It should be tested, of course.

I would defer to Sean to make the patch on top of mine :-)

-- 
Josh

  reply	other threads:[~2019-07-18 14:12 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-18  1:36 [PATCH v2 00/22] x86, objtool: several fixes/improvements Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 01/22] x86/paravirt: Fix callee-saved function ELF sizes Josh Poimboeuf
2019-07-18 19:07   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 02/22] x86/kvm: Fix fastop function ELF metadata Josh Poimboeuf
2019-07-18 19:08   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 03/22] x86/kvm: Replace vmx_vmenter()'s call to kvm_spurious_fault() with UD2 Josh Poimboeuf
2019-07-18  8:17   ` Paolo Bonzini
2019-07-18 19:08   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 04/22] x86/kvm: Don't call kvm_spurious_fault() from .fixup Josh Poimboeuf
2019-07-18  8:22   ` Paolo Bonzini
2019-07-18 13:16     ` Sean Christopherson
2019-07-18 13:18       ` Paolo Bonzini
2019-07-18 14:12         ` Josh Poimboeuf [this message]
2019-07-18 14:13           ` Paolo Bonzini
2019-07-18 14:03       ` Josh Poimboeuf
2019-07-18 19:09   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 05/22] x86/entry: Fix thunk function ELF sizes Josh Poimboeuf
2019-07-18 19:10   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 06/22] x86/head/64: Annotate start_cpu0() as non-callable Josh Poimboeuf
2019-07-18 19:11   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 07/22] x86/uaccess: Remove ELF function annotation from copy_user_handle_tail() Josh Poimboeuf
2019-07-18 19:11   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 08/22] x86/uaccess: Don't leak AC flag into fentry from mcsafe_handle_tail() Josh Poimboeuf
2019-07-18 19:12   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 09/22] x86/uaccess: Remove redundant CLACs in getuser/putuser error paths Josh Poimboeuf
2019-07-18 19:13   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 10/22] bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() Josh Poimboeuf
2019-07-18 19:14   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2020-04-29 21:51     ` BPF vs objtool again Josh Poimboeuf
2020-04-29 22:01       ` Arvind Sankar
2020-04-29 23:41       ` Alexei Starovoitov
2020-04-30  0:13         ` Josh Poimboeuf
2020-04-30  2:10           ` Alexei Starovoitov
2020-04-30  3:53             ` Josh Poimboeuf
2020-04-30  4:24               ` Alexei Starovoitov
2020-04-30  4:43                 ` Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 11/22] objtool: Add mcsafe_handle_tail() to the uaccess safe list Josh Poimboeuf
2019-07-18 19:14   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 12/22] objtool: Track original function across branches Josh Poimboeuf
2019-07-18 19:15   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 13/22] objtool: Refactor function alias logic Josh Poimboeuf
2019-07-18 19:16   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 14/22] objtool: Warn on zero-length functions Josh Poimboeuf
2019-07-18 19:17   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 15/22] objtool: Change dead_end_function() to return boolean Josh Poimboeuf
2019-07-18 19:17   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 16/22] objtool: Do frame pointer check before dead end check Josh Poimboeuf
2019-07-18 19:18   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 17/22] objtool: Refactor sibling call detection logic Josh Poimboeuf
2019-07-18 19:19   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 18/22] objtool: Refactor jump table code Josh Poimboeuf
2019-07-18 19:20   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 19/22] objtool: Support repeated uses of the same C jump table Josh Poimboeuf
2019-07-18 19:20   ` [tip:core/urgent] " tip-bot for Jann Horn
2019-07-18  1:36 ` [PATCH v2 20/22] objtool: Fix seg fault on bad switch table entry Josh Poimboeuf
2019-07-18 19:21   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 21/22] objtool: convert insn type to enum Josh Poimboeuf
2019-07-18 19:22   ` [tip:core/urgent] objtool: Convert " tip-bot for Josh Poimboeuf
2019-07-18  1:36 ` [PATCH v2 22/22] objtool: Support conditional retpolines Josh Poimboeuf
2019-07-18 19:23   ` [tip:core/urgent] " tip-bot for Josh Poimboeuf

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