From: Peter Zijlstra <peterz@infradead.org>
To: Sean Christopherson <seanjc@google.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
jpoimboe@redhat.com, mark.rutland@arm.com, dvyukov@google.com,
pbonzini@redhat.com, mbenes@suse.cz
Subject: Re: [RFC][PATCH 15/22] x86,vmx: Remove .fixup usage
Date: Fri, 5 Nov 2021 21:58:05 +0100 [thread overview]
Message-ID: <20211105205805.GR174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <YYV1UeFeWUtnQ4jV@google.com>
On Fri, Nov 05, 2021 at 06:17:53PM +0000, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/vmx/vmx_ops.h b/arch/x86/kvm/vmx/vmx_ops.h
> index 9e9ef47e988c..5e5113d2b324 100644
> --- a/arch/x86/kvm/vmx/vmx_ops.h
> +++ b/arch/x86/kvm/vmx/vmx_ops.h
> @@ -76,29 +75,24 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
> "ja 3f\n\t"
>
> /*
> - * VMREAD failed. Push '0' for @fault, push the failing
> - * @field, and bounce through the trampoline to preserve
> - * volatile registers.
> + * VMREAD failed, push the failing @field, and bounce
> + * through the trampoline to preserve volatile registers.
> + * If VMREAD faults, this will push -FAULT (see below).
> */
> - "push $0\n\t"
> - "push %2\n\t"
> - "2:call vmread_error_trampoline\n\t"
> + "2: push %2\n\t"
> + "call vmread_error_trampoline\n\t"
>
> /*
> * Unwind the stack. Note, the trampoline zeros out the
> - * memory for @fault so that the result is '0' on error.
> + * memory for @field so that the result is '0' on error,
> + * hence the pop to %1, not %2.
> */
> - "pop %2\n\t"
> "pop %1\n\t"
> "3:\n\t"
>
> - /* VMREAD faulted. As above, except push '1' for @fault. */
> - ".pushsection .fixup, \"ax\"\n\t"
> - "4: push $1\n\t"
> - "push %2\n\t"
> - "jmp 2b\n\t"
> - ".popsection\n\t"
> - _ASM_EXTABLE(1b, 4b)
> + /* VMREAD faulted. As above, except push '-EFAULT' for @fault. */
> + _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, %1)
> +
> : ASM_CALL_CONSTRAINT, "=r"(value) : "r"(field) : "cc");
> return value;
> }
A different option is something like the below; down side is that it
increases the amount of text, while your version decreases the amount of
useless text (the gunk between vmread and 3:, all of which should
ideally live out-of-line).
For now I'll stick with your patch.
diff --git a/arch/x86/kvm/vmx/vmx_ops.h b/arch/x86/kvm/vmx/vmx_ops.h
index 9e9ef47e988c..99fc1f34fbd4 100644
--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@@ -81,8 +81,8 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
* volatile registers.
*/
"push $0\n\t"
- "push %2\n\t"
- "2:call vmread_error_trampoline\n\t"
+ "2: push %2\n\t"
+ "call vmread_error_trampoline\n\t"
/*
* Unwind the stack. Note, the trampoline zeros out the
@@ -90,14 +90,14 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
*/
"pop %2\n\t"
"pop %1\n\t"
- "3:\n\t"
+ "jmp 3f\n\t"
- /* VMREAD faulted. As above, except push '1' for @fault. */
- ".pushsection .fixup, \"ax\"\n\t"
"4: push $1\n\t"
- "push %2\n\t"
"jmp 2b\n\t"
- ".popsection\n\t"
+
+ "3:\n\t"
+
+ /* VMREAD faulted. As above, except push '1' for @fault. */
_ASM_EXTABLE(1b, 4b)
: ASM_CALL_CONSTRAINT, "=r"(value) : "r"(field) : "cc");
return value;
next prev parent reply other threads:[~2021-11-05 21:03 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-04 16:47 [RFC][PATCH 00/22] x86: Remove anonymous out-of-line fixups Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 01/22] bitfield.h: Fix "type of reg too small for mask" test Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 02/22] x86,mmx_32: Remove .fixup usage Peter Zijlstra
2021-11-04 18:00 ` Borislav Petkov
2021-11-05 11:20 ` David Laight
2021-11-04 20:22 ` Josh Poimboeuf
2021-11-05 8:05 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 03/22] x86,copy_user_64: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 04/22] x86,copy_mc_64: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 05/22] x86,entry_64: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 06/22] x86,entry_32: " Peter Zijlstra
2021-11-04 20:39 ` Josh Poimboeuf
2021-11-05 7:43 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 07/22] x86,extable: Extend extable functionality Peter Zijlstra
2021-11-04 21:49 ` Josh Poimboeuf
2021-11-05 7:54 ` Peter Zijlstra
2021-11-05 10:16 ` Mark Rutland
2021-11-05 17:32 ` Sean Christopherson
2021-11-05 18:45 ` Peter Zijlstra
2021-11-05 19:17 ` Sean Christopherson
2021-11-05 19:32 ` Peter Zijlstra
2021-11-05 19:47 ` Sean Christopherson
2021-11-05 20:15 ` Peter Zijlstra
2021-11-05 20:26 ` Peter Zijlstra
2021-11-05 22:30 ` Sean Christopherson
2021-11-04 16:47 ` [RFC][PATCH 08/22] x86,msr: Remove .fixup usage Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 09/22] x86,futex: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 10/22] x86,uaccess: " Peter Zijlstra
2021-11-04 22:28 ` Josh Poimboeuf
2021-11-04 16:47 ` [RFC][PATCH 11/22] x86,xen: " Peter Zijlstra
2021-11-04 22:31 ` Josh Poimboeuf
2021-11-05 7:56 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 12/22] x86,fpu: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 13/22] x86,segment: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 14/22] x86,ftrace: " Peter Zijlstra
2021-11-04 22:35 ` Josh Poimboeuf
2021-11-05 7:57 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 15/22] x86,vmx: " Peter Zijlstra
2021-11-04 18:50 ` Paolo Bonzini
2021-11-05 18:17 ` Sean Christopherson
2021-11-05 18:52 ` Peter Zijlstra
2021-11-05 20:58 ` Peter Zijlstra [this message]
2021-11-05 22:29 ` Sean Christopherson
2021-11-06 7:05 ` Paolo Bonzini
2021-11-06 8:36 ` Peter Zijlstra
2021-11-07 19:13 ` Paolo Bonzini
2021-11-06 8:28 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 16/22] x86,checksum_32: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 17/22] x86,sgx: " Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 18/22] x86,kvm: " Peter Zijlstra
2021-11-04 18:50 ` Paolo Bonzini
2021-11-05 7:58 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 19/22] x86,usercopy_32: Simplify Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 20/22] x86,usercopy: Remove .fixup usage Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 21/22] x86,word-at-a-time: " Peter Zijlstra
2021-11-04 23:33 ` Josh Poimboeuf
2021-11-05 8:04 ` Peter Zijlstra
2021-11-04 16:47 ` [RFC][PATCH 22/22] x86: Remove .fixup section Peter Zijlstra
2021-11-04 23:00 ` Josh Poimboeuf
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