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Groups > linux.kernel > #1534870
| From | Andrew Cooper <andrew.cooper3@citrix.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation |
| Date | 2016-12-02 12:50 +0100 |
| Message-ID | <sJUvM-3hJ-31@gated-at.bofh.it> (permalink) |
| References | <sJK3o-4BW-19@gated-at.bofh.it> <sJK3n-4BW-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 02/12/16 00:35, Andy Lutomirski wrote:
> On Xen PV, CPUID is likely to trap, and Xen hypercalls aren't
> guaranteed to serialize. (Even CPUID isn't *really* guaranteed to
> serialize on Xen PV, but, in practice, any trap it generates will
> serialize.)
Well, Xen will enabled CPUID Faulting wherever it can, which is
realistically all IvyBridge hardware and newer.
All hypercalls are a privilege change to cpl0. I'd hope this condition
is serialising, but I can't actually find any documentation proving or
disproving this.
>
> On my laptop, CPUID(eax=1, ecx=0) is ~83ns and IRET-to-self is
> ~110ns. But Xen PV will trap CPUID if possible, so IRET-to-self
> should end up being a nice speedup.
>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
CC'ing xen-devel and the Xen maintainers in Linux.
As this is the only email from this series in my inbox, I will say this
here, but it should really be against patch 6.
A write to %cr2 is apparently (http://sandpile.org/x86/coherent.htm) not
serialising on the 486, but I don't have a manual to hand to check.
~Andrew
> ---
> arch/x86/xen/enlighten.c | 35 +++++++++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index bdd855685403..1f765b41eee7 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -311,6 +311,39 @@ static __read_mostly unsigned int cpuid_leaf1_ecx_set_mask;
> static __read_mostly unsigned int cpuid_leaf5_ecx_val;
> static __read_mostly unsigned int cpuid_leaf5_edx_val;
>
> +static void xen_sync_core(void)
> +{
> + register void *__sp asm(_ASM_SP);
> +
> +#ifdef CONFIG_X86_32
> + asm volatile (
> + "pushl %%ss\n\t"
> + "pushl %%esp\n\t"
> + "addl $4, (%%esp)\n\t"
> + "pushfl\n\t"
> + "pushl %%cs\n\t"
> + "pushl $1f\n\t"
> + "iret\n\t"
> + "1:"
> + : "+r" (__sp) : : "cc");
> +#else
> + unsigned long tmp;
> +
> + asm volatile (
> + "movq %%ss, %0\n\t"
> + "pushq %0\n\t"
> + "pushq %%rsp\n\t"
> + "addq $8, (%%rsp)\n\t"
> + "pushfq\n\t"
> + "movq %%cs, %0\n\t"
> + "pushq %0\n\t"
> + "pushq $1f\n\t"
> + "iretq\n\t"
> + "1:"
> + : "=r" (tmp), "+r" (__sp) : : "cc");
> +#endif
> +}
> +
> static void xen_cpuid(unsigned int *ax, unsigned int *bx,
> unsigned int *cx, unsigned int *dx)
> {
> @@ -1289,6 +1322,8 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
>
> .start_context_switch = paravirt_start_context_switch,
> .end_context_switch = xen_end_context_switch,
> +
> + .sync_core = xen_sync_core,
> };
>
> static void xen_reboot(int reason)
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[PATCH 0/4] CPUID-less CPU fixes and improvements Andy Lutomirski <luto@kernel.org> - 2016-11-30 21:40 +0100
[PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Andy Lutomirski <luto@kernel.org> - 2016-11-30 21:40 +0100
Re: [PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Borislav Petkov <bp@alien8.de> - 2016-12-01 10:30 +0100
Re: [PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Andy Lutomirski <luto@amacapital.net> - 2016-12-01 18:10 +0100
Re: [PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Andrew Cooper <andrew.cooper3@citrix.com> - 2016-12-01 18:50 +0100
Re: [PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Ingo Molnar <mingo@kernel.org> - 2016-12-02 08:40 +0100
[PATCH 3/4] x86/microcode/intel: Replace sync_core() with cpuid_eax(1) Andy Lutomirski <luto@kernel.org> - 2016-11-30 21:40 +0100
Re: [PATCH 3/4] x86/microcode/intel: Replace sync_core() with cpuid_eax(1) Borislav Petkov <bp@alien8.de> - 2016-12-01 10:20 +0100
[PATCH v2 6/6] x86/asm: Change sync_core() to use MOV to CR2 to serialize Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
[PATCH v2 4/6] x86/paravirt: Make sync_core() be a paravirt op Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
[PATCH v2 3/6] x86/microcode/intel: Replace sync_core() with cpuid_eax(1) Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
[PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andrew Cooper <andrew.cooper3@citrix.com> - 2016-12-02 12:50 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-02 18:10 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andrew Cooper <andrew.cooper3@citrix.com> - 2016-12-02 18:20 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andrew Cooper <andrew.cooper3@citrix.com> - 2016-12-02 18:30 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-02 18:30 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-12-02 19:50 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-02 20:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-12-02 21:10 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 18:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@kernel.org> - 2016-12-02 18:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Borislav Petkov <bp@kernel.org> - 2016-12-02 19:20 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 19:30 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Borislav Petkov <bp@kernel.org> - 2016-12-02 20:00 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 20:10 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 20:30 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Borislav Petkov <bp@alien8.de> - 2016-12-02 20:30 +0100
[PATCH] x86/alternatives: Do not use sync_core() to serialize I$ Borislav Petkov <bp@alien8.de> - 2016-12-03 16:10 +0100
Re: [PATCH] x86/alternatives: Do not use sync_core() to serialize I$ Andy Lutomirski <luto@amacapital.net> - 2016-12-03 18:20 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 20:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-02 21:50 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 22:20 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-03 00:00 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-03 00:20 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-02 20:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski <luto@amacapital.net> - 2016-12-02 20:30 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Borislav Petkov <bp@alien8.de> - 2016-12-02 20:40 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Borislav Petkov <bp@alien8.de> - 2016-12-02 20:30 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 19:20 +0100
Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Borislav Petkov <bp@alien8.de> - 2016-12-03 13:50 +0100
[PATCH v2 2/6] Revert "x86/boot: Fail the boot if !M486 and CPUID is missing" Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
Re: [PATCH 0/4] CPUID-less CPU fixes and improvements Andy Lutomirski <luto@amacapital.net> - 2016-12-02 01:40 +0100
Re: [PATCH 0/4] CPUID-less CPU fixes and improvements Ingo Molnar <mingo@kernel.org> - 2016-12-02 11:20 +0100
[PATCH v2 0/6] CPUID-less CPU/sync_core fixes and improvements Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
[PATCH v2 1/6] x86/asm/32: Make sync_core() handle missing CPUID on all 32-bit kernels Andy Lutomirski <luto@kernel.org> - 2016-12-02 01:40 +0100
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