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Re: [Xen-devel] [PATCH v1] restore the fake x2apic value for cpuid
- To: Xin Li <talons.lee@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxx
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 3 Dec 2018 08:00:45 +0100
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- Cc: Talons Lee <xin.li@xxxxxxxxxx>, Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
- Delivery-date: Mon, 03 Dec 2018 07:00:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 22/11/2018 08:18, Xin Li wrote:
> From: Talons Lee <xin.li@xxxxxxxxxx>
>
> Commit e657fcc clears cpu x2apic capability bit instead of using fake
> cpuid value. However, with cpuid x2apic bit on, xen_read_msr_safe() will
> not clear the EXTD bit, which leads to uncessary msr write trying to
> disable x2apic in __x2apic_disable(). So restore the fake x2apic value.
>
> Signed-off-by: Talons Lee <xin.li@xxxxxxxxxx>
Wouldn't it be easier to use just rdmsr_safe() in __x2apic_disable()
instead?
Juergen
>
> ---
> CC: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> CC: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
>
> ---
> arch/x86/xen/enlighten_pv.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 4b20082..156c408 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -165,12 +165,17 @@ static void xen_cpuid(unsigned int *ax, unsigned int
> *bx,
> unsigned int *cx, unsigned int *dx)
> {
> unsigned maskebx = ~0;
> + unsigned maskecx = ~0;
>
> /*
> * Mask out inconvenient features, to try and disable as many
> * unsupported kernel subsystems as possible.
> */
> switch (*ax) {
> + case 1:
> + maskecx &= ~(1 << (X86_FEATURE_X2APIC % 32));
> + break;
> +
> case CPUID_MWAIT_LEAF:
> /* Synthesize the values.. */
> *ax = 0;
> @@ -193,6 +198,7 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
> : "0" (*ax), "2" (*cx));
>
> *bx &= maskebx;
> + *cx &= maskecx;
> }
> STACK_FRAME_NON_STANDARD(xen_cpuid); /* XEN_EMULATE_PREFIX */
>
>
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