From: Borislav Petkov <bp@alien8.de>
To: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org, peterz@infradead.org,
luto@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 07/12] x86: add new features for paravirt patching
Date: Tue, 8 Dec 2020 19:43:15 +0100 [thread overview]
Message-ID: <20201208184315.GE27920@zn.tnic> (raw)
In-Reply-To: <20201120114630.13552-8-jgross@suse.com>
On Fri, Nov 20, 2020 at 12:46:25PM +0100, Juergen Gross wrote:
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index dad350d42ecf..ffa23c655412 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -237,6 +237,9 @@
> #define X86_FEATURE_VMCALL ( 8*32+18) /* "" Hypervisor supports the VMCALL instruction */
> #define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
> #define X86_FEATURE_SEV_ES ( 8*32+20) /* AMD Secure Encrypted Virtualization - Encrypted State */
> +#define X86_FEATURE_NOT_XENPV ( 8*32+21) /* "" Inverse of X86_FEATURE_XENPV */
> +#define X86_FEATURE_NO_PVUNLOCK ( 8*32+22) /* "" No PV unlock function */
> +#define X86_FEATURE_NO_VCPUPREEMPT ( 8*32+23) /* "" No PV vcpu_is_preempted function */
Ew, negative features. ;-\
/me goes forward and looks at usage sites:
+ ALTERNATIVE_2 "jmp *paravirt_iret(%rip);", \
+ "jmp native_iret;", X86_FEATURE_NOT_XENPV, \
+ "jmp xen_iret;", X86_FEATURE_XENPV
Can we make that:
ALTERNATIVE_TERNARY "jmp *paravirt_iret(%rip);",
"jmp xen_iret;", X86_FEATURE_XENPV,
"jmp native_iret;", X86_FEATURE_XENPV,
where the last two lines are supposed to mean
X86_FEATURE_XENPV ? "jmp xen_iret;" : "jmp native_iret;"
Now, in order to convey that logic to apply_alternatives(), you can do:
struct alt_instr {
s32 instr_offset; /* original instruction */
s32 repl_offset; /* offset to replacement instruction */
u16 cpuid; /* cpuid bit set for replacement */
u8 instrlen; /* length of original instruction */
u8 replacementlen; /* length of new instruction */
u8 padlen; /* length of build-time padding */
u8 flags; /* patching flags */ <--- THIS
} __packed;
and yes, we have had the flags thing in a lot of WIP diffs over the
years but we've never come to actually needing it.
Anyway, then, apply_alternatives() will do:
if (flags & ALT_NOT_FEATURE)
or something like that - I'm bad at naming stuff - then it should patch
only when the feature is NOT set and vice versa.
There in that
if (!boot_cpu_has(a->cpuid)) {
branch.
Hmm?
> /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
> #define X86_FEATURE_FSGSBASE ( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 2400ad62f330..f8f9700719cf 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -593,6 +593,18 @@ int alternatives_text_reserved(void *start, void *end)
> #endif /* CONFIG_SMP */
>
> #ifdef CONFIG_PARAVIRT
> +static void __init paravirt_set_cap(void)
> +{
> + if (!boot_cpu_has(X86_FEATURE_XENPV))
> + setup_force_cpu_cap(X86_FEATURE_NOT_XENPV);
> +
> + if (pv_is_native_spin_unlock())
> + setup_force_cpu_cap(X86_FEATURE_NO_PVUNLOCK);
> +
> + if (pv_is_native_vcpu_is_preempted())
> + setup_force_cpu_cap(X86_FEATURE_NO_VCPUPREEMPT);
> +}
> +
> void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
> struct paravirt_patch_site *end)
> {
> @@ -616,6 +628,8 @@ void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
> }
> extern struct paravirt_patch_site __start_parainstructions[],
> __stop_parainstructions[];
> +#else
> +static void __init paravirt_set_cap(void) { }
> #endif /* CONFIG_PARAVIRT */
>
> /*
> @@ -723,6 +737,18 @@ void __init alternative_instructions(void)
> * patching.
> */
>
> + paravirt_set_cap();
Can that be called from somewhere in the Xen init path and not from
here? Somewhere before check_bugs() gets called.
> + /*
> + * First patch paravirt functions, such that we overwrite the indirect
> + * call with the direct call.
> + */
> + apply_paravirt(__parainstructions, __parainstructions_end);
> +
> + /*
> + * Then patch alternatives, such that those paravirt calls that are in
> + * alternatives can be overwritten by their immediate fragments.
> + */
> apply_alternatives(__alt_instructions, __alt_instructions_end);
Can you give an example here pls why the paravirt patching needs to run
first?
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-12-08 18:43 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 11:46 [PATCH v2 00/12] x86: major paravirt cleanup Juergen Gross
2020-11-20 11:46 ` [PATCH v2 01/12] x86/xen: use specific Xen pv interrupt entry for MCE Juergen Gross
2020-12-09 21:03 ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 02/12] x86/xen: use specific Xen pv interrupt entry for DF Juergen Gross
2020-12-09 21:03 ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 03/12] x86/pv: switch SWAPGS to ALTERNATIVE Juergen Gross
2020-11-27 11:31 ` Borislav Petkov
2020-12-09 21:07 ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call Juergen Gross
2020-12-02 12:32 ` Borislav Petkov
2020-12-02 14:48 ` Jürgen Groß
2020-12-02 17:08 ` Borislav Petkov
2020-11-20 11:46 ` [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Juergen Gross
2020-11-20 11:59 ` Peter Zijlstra
2020-11-20 12:05 ` Jürgen Groß
2020-11-22 6:55 ` Jürgen Groß
2020-11-22 21:44 ` Andy Lutomirski
2020-11-23 5:21 ` Jürgen Groß
2020-11-23 15:15 ` Andy Lutomirski
2020-12-09 13:27 ` Mark Rutland
2020-12-09 14:02 ` Mark Rutland
2020-12-09 14:05 ` Jürgen Groß
2020-12-09 18:15 ` Mark Rutland
2020-12-09 18:54 ` Thomas Gleixner
2020-12-10 11:10 ` Mark Rutland
2020-12-10 20:15 ` x86/ioapic: Cleanup the timer_works() irqflags mess Thomas Gleixner
2020-12-11 5:10 ` Jürgen Groß
2020-11-27 2:20 ` [x86] 97e8f0134a: fio.write_iops 8.6% improvement kernel test robot
2020-11-20 11:46 ` [PATCH v2 06/12] x86/paravirt: switch time pvops functions to use static_call() Juergen Gross
2020-11-20 12:01 ` Peter Zijlstra
2020-11-20 12:07 ` Jürgen Groß
2020-11-20 11:46 ` [PATCH v2 07/12] x86: add new features for paravirt patching Juergen Gross
2020-12-08 18:43 ` Borislav Petkov [this message]
2020-12-09 7:30 ` Jürgen Groß
2020-12-09 12:03 ` Borislav Petkov
2020-12-09 12:22 ` Jürgen Groß
2020-12-10 17:58 ` Borislav Petkov
2020-11-20 11:46 ` [PATCH v2 08/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross
2020-11-20 12:08 ` Peter Zijlstra
2020-11-20 12:16 ` Jürgen Groß
2020-11-20 16:52 ` Arvind Sankar
2020-11-20 11:46 ` [PATCH v2 09/12] x86/paravirt: switch iret pvops to ALTERNATIVE Juergen Gross
2020-11-20 11:46 ` [PATCH v2 10/12] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross
2020-11-20 11:46 ` [PATCH v2 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross
2020-11-20 15:46 ` kernel test robot
2020-11-25 15:46 ` [x86/paravirt] fd8d46a7a2: kernel-selftests.livepatch.test-callbacks.sh.fail kernel test robot
2020-11-20 11:46 ` [PATCH v2 12/12] x86/paravirt: have only one paravirt patch function Juergen Gross
2020-11-20 14:18 ` kernel test robot
2020-11-20 12:53 ` [PATCH v2 00/12] x86: major paravirt cleanup Peter Zijlstra
2020-11-23 13:43 ` Peter Zijlstra
2020-12-15 11:42 ` Jürgen Groß
2020-12-15 14:18 ` Peter Zijlstra
2020-12-15 14:54 ` Peter Zijlstra
2020-12-15 15:07 ` Jürgen Groß
2020-12-16 0:38 ` Josh Poimboeuf
2020-12-16 8:40 ` Peter Zijlstra
2020-12-16 16:56 ` Josh Poimboeuf
2020-12-16 17:58 ` Peter Zijlstra
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