From: Jork Loeser <Jork.Loeser@microsoft.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "x86@kernel.org" <x86@kernel.org>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "KY Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Steven Rostedt <rostedt@goodmis.org>
Subject: RE: [PATCH 6/7] x86/hyper-v: use hypercall for remove TLB flush
Thread-Topic: [PATCH 6/7] x86/hyper-v: use hypercall for remove TLB flush
Thread-Index: AQHSr5Hv7dIOzBIb8EGcRSIrNTRi16G6VNRg
Date: Fri, 7 Apr 2017 20:46:13 +0000
Message-ID: <MWHPR21MB063911897C6E0286F3055A56F10C0@MWHPR21MB0639.namprd21.prod.outlook.com>
References: <20170407112701.17157-1-vkuznets@redhat.com>
 <20170407112701.17157-7-vkuznets@redhat.com>
In-Reply-To: <20170407112701.17157-7-vkuznets@redhat.com>
Accept-Language: en-US
Content-Language: en-US
spamdiagnosticoutput: 1:99
spamdiagnosticmetadata: NSPM
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-originalarrivaltime: 07 Apr 2017 20:46:13.3644
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR21MB0639
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v37KkUHk022885
Content-Length: 2485
Lines: 76

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
> Sent: Friday, April 7, 2017 04:27
> To: devel@linuxdriverproject.org; x86@kernel.org
> Cc: linux-kernel@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
> Haiyang Zhang <haiyangz@microsoft.com>; Stephen Hemminger
> <sthemmin@microsoft.com>; Thomas Gleixner <tglx@linutronix.de>; Ingo
> Molnar <mingo@redhat.com>; H. Peter Anvin <hpa@zytor.com>; Steven
> Rostedt <rostedt@goodmis.org>; Jork Loeser <Jork.Loeser@microsoft.com>
> Subject: [PATCH 6/7] x86/hyper-v: use hypercall for remove TLB flush

> diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c new file
> mode 100644 index 0000000..fb487cb
> --- /dev/null
> +++ b/arch/x86/hyperv/mmu.c
> @@ -0,0 +1,128 @@
> +#include <linux/types.h>
> +#include <linux/hyperv.h>
> +#include <linux/slab.h>
> +#include <asm/mshyperv.h>
> +#include <asm/tlbflush.h>
> +#include <asm/msr.h>
> +#include <asm/fpu/api.h>
> +
> +/*
> + * Arbitrary number; we need to pre-allocate per-cpu struct for doing
> +TLB
> + * flush hypercalls and we need to pick a size. '16' means we'll be
> +able
> + * to flush 16 * 4096 pages (256MB) with one hypercall.
> + */
> +#define HV_MMU_MAX_GVAS 16
> +
> +/* HvFlushVirtualAddressSpace*, HvFlushVirtualAddressList hypercalls */
> +struct hv_flush_pcpu {
> +	struct {
> +		__u64 address_space;
> +		__u64 flags;
> +		__u64 processor_mask;
> +		__u64 gva_list[HV_MMU_MAX_GVAS];
> +	} flush;
> +
> +	spinlock_t lock;
> +};
Does this need an alignment declaration, so that the flush portion never crosses a page boundary when allocated with alloc_percpu()?

> +
> +static struct hv_flush_pcpu __percpu *pcpu_flush;
> +
> +static void hyperv_flush_tlb_others(const struct cpumask *cpus,
> +				    struct mm_struct *mm, unsigned long
> start,
> +				    unsigned long end)
> +{
> +	struct hv_flush_pcpu *flush;
> +	unsigned long cur, flags;
> +	u64 status = -1ULL;
> +	int cpu, vcpu, gva_n;
> +
> +	if (!pcpu_flush || !hv_hypercall_pg)
> +		goto do_native;
> +
> +	if (cpumask_empty(cpus))
> +		return;
> +
> +	flush = this_cpu_ptr(pcpu_flush);
> +	spin_lock_irqsave(&flush->lock, flags);

What purpose does the spinlock on the CPU-local struct serve? Would a local_irq_save() do?

Could this be called from NMI context, such as from the debugger?

Could this be a long-running loop, e.g. due to a large start/end range? If so, consider disabling interrupts only in the inner loop / flush the entire space?

Regards,
Jork