From: "Jürgen Groß" <jgross@suse.com>
To: Borislav Petkov <bp@alien8.de>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Deep Shah <sdeep@vmware.com>,
"VMware, Inc." <pv-drivers@vmware.com>
Subject: Re: [PATCH v5 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE
Date: Tue, 9 Mar 2021 07:21:35 +0100 [thread overview]
Message-ID: <09410a65-a5dc-db76-d867-f6b0b968323f@suse.com> (raw)
In-Reply-To: <20210308183058.GC12548@zn.tnic>
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On 08.03.21 19:30, Borislav Petkov wrote:
> On Mon, Mar 08, 2021 at 01:28:43PM +0100, Juergen Gross wrote:
>> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
>> index 36cd71fa097f..04b3067f31b5 100644
>> --- a/arch/x86/include/asm/paravirt.h
>> +++ b/arch/x86/include/asm/paravirt.h
>> @@ -137,7 +137,8 @@ static inline void write_cr0(unsigned long x)
>>
>> static inline unsigned long read_cr2(void)
>> {
>> - return PVOP_CALLEE0(unsigned long, mmu.read_cr2);
>> + return PVOP_ALT_CALLEE0(unsigned long, mmu.read_cr2,
>> + "mov %%cr2, %%rax;", ~X86_FEATURE_XENPV);
>
> Just some cursory poking first - indepth review later.
>
> Do I see this correctly that the negated feature can be expressed with, to use
> this example here:
>
> ALTERNATIVE_TERNARY(mmu.read_cr2, X86_FEATURE_XENPV, "", "mov %%cr2, %%rax;");
>
> ?
No.
This would leave the Xen-pv case with a nop, while we need it to call
mmu.read_cr2().
In the Xen-pv case there must be _no_ alternative patching in order to
have the paravirt patching do its patching (indirect->direct call).
This is exactly the reason why I need to "not feature".
The only other solution I can think of would be a "split static_call"
handling using ALTERNATIVE_TERNARY():
ALTERNATIVE_TERNARY(initial_static_call(mmu.read_cr2),
X86_FEATURE_XENPV,
final_static_call(mmu.read_cr2),
"mov %%cr2, %%rax;");
with initial_static_call() doing an indirect call, while
final_static_call() would do a direct call.
Not sure we really want that.
Juergen
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next prev parent reply other threads:[~2021-03-09 6:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 12:28 [PATCH v5 00/12] x86: major paravirt cleanup Juergen Gross
2021-03-08 12:28 ` [PATCH v5 01/12] staticcall: move struct static_call_key definition to static_call_types.h Juergen Gross
2021-03-08 16:27 ` Peter Zijlstra
2021-03-08 12:28 ` [PATCH v5 02/12] x86/paravirt: switch time pvops functions to use static_call() Juergen Gross
2021-03-08 17:00 ` Boris Ostrovsky
2021-03-09 6:14 ` Jürgen Groß
2021-03-08 12:28 ` [PATCH v5 03/12] x86/alternative: drop feature parameter from ALTINSTR_REPLACEMENT() Juergen Gross
2021-03-08 12:28 ` [PATCH v5 04/12] x86/alternative: support not-feature Juergen Gross
2021-03-08 12:28 ` [PATCH v5 05/12] x86/alternative: support ALTERNATIVE_TERNARY Juergen Gross
2021-03-08 12:28 ` [PATCH v5 06/12] x86: add new features for paravirt patching Juergen Gross
2021-03-08 12:28 ` [PATCH v5 07/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross
2021-03-08 12:28 ` [PATCH v5 08/12] x86/paravirt: simplify paravirt macros Juergen Gross
2021-03-08 12:28 ` [PATCH v5 09/12] x86/paravirt: switch iret pvops to ALTERNATIVE Juergen Gross
2021-03-08 12:28 ` [PATCH v5 10/12] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross
2021-03-08 12:28 ` [PATCH v5 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross
2021-03-08 18:30 ` Borislav Petkov
2021-03-09 6:21 ` Jürgen Groß [this message]
2021-03-08 12:28 ` [PATCH v5 12/12] x86/paravirt: have only one paravirt patch function Juergen Gross
2021-03-08 16:31 ` [PATCH v5 00/12] x86: major paravirt cleanup Peter Zijlstra
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