linux-kernel - RE: [RFC Patch 1/3] X86/Hyper-V: Add flush HvFlushGuestPhysicalAddressSpace hypercall support

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Message-ID: <SN6PR2101MB11204AF2E43FF4C91B326FFDDC660@SN6PR2101MB1120.namprd21.prod.outlook.com>
Date:   Tue, 5 Jun 2018 16:59:11 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Tianyu Lan <Tianyu.Lan@...rosoft.com>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>
Subject: RE: [RFC Patch 1/3] X86/Hyper-V: Add flush
 HvFlushGuestPhysicalAddressSpace hypercall support

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> On Behalf
> Of Tianyu Lan
> Sent: Monday, June 4, 2018 2:08 AM
> Cc: Tianyu Lan <Tianyu.Lan@...rosoft.com>; KY Srinivasan <kys@...rosoft.com>; Haiyang
> Zhang <haiyangz@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>;
> tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; x86@...nel.org;
> pbonzini@...hat.com; rkrcmar@...hat.com; devel@...uxdriverproject.org; linux-
> kernel@...r.kernel.org; kvm@...r.kernel.org; vkuznets@...hat.com
> Subject: [RFC Patch 1/3] X86/Hyper-V: Add flush HvFlushGuestPhysicalAddressSpace hypercall
> support
> 
> Hyper-V provides a pv hypercall HvFlushGuestPhysicalAddressSpace to flush
> nested VM address space mapping in l1 hypervisor and it's to reduce overhead
> of flushing ept tlb among vcpus. This patch is to implement it.
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> ---
> diff --git a/arch/x86/hyperv/nested.c b/arch/x86/hyperv/nested.c
> new file mode 100644
> index 000000000000..17f7c288eccc
> --- /dev/null
> +++ b/arch/x86/hyperv/nested.c
> +#include <linux/types.h>
> +#include <asm/hyperv-tlfs.h>
> +#include <asm/mshyperv.h>
> +#include <asm/tlbflush.h>
> +
> +int hyperv_flush_guest_mapping(u64 as)
> +{
> +	struct hv_guest_mapping_flush **flush_pcpu;
> +	struct hv_guest_mapping_flush *flush;
> +	u64 status = U64_MAX;

Initializing status to U64_MAX doesn't seem necessary.

> +	unsigned long flags;
> +	int ret = -EFAULT;
> +
> +	if (!hv_hypercall_pg)
> +		goto fault;
> +
> +	local_irq_save(flags);
> +
> +	flush_pcpu = (struct hv_guest_mapping_flush **)
> +		this_cpu_ptr(hyperv_pcpu_input_arg);
> +
> +	flush = *flush_pcpu;
> +
> +	if (unlikely(!flush)) {
> +		local_irq_restore(flags);
> +		goto fault;
> +	}
> +
> +	flush->address_space = as;
> +	flush->flags = 0;
> +
> +	status = hv_do_hypercall(HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE,
> +				 flush, NULL);
> +	local_irq_restore(flags);
> +
> +	if (!(status & HV_HYPERCALL_RESULT_MASK))
> +		ret = 0;
> +
> +fault:
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(hyperv_flush_guest_mapping);
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index b8c89265baf0..53bbeb08faea 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -309,6 +309,7 @@ struct ms_hyperv_tsc_page {
>  #define HV_X64_MSR_REENLIGHTENMENT_CONTROL	0x40000106
> 
>  /* Nested features (CPUID 0x4000000A) EAX */
> +#define HV_X64_NESTED_GUSET_MAPPING_FLUSH	BIT(18)

The #define name is misspelled.  "_GUSET_" should be "_GUEST_".
And the matching usage in patch 3/3 will need to be updated as well.

Michael