linux-kernel - Re: [PATCH v6 06/12] Add PV MSR to enable asynchronous page faults delivery.

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Date:	Thu, 7 Oct 2010 19:53:29 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org, mtosatti@...hat.com
Subject: Re: [PATCH v6 06/12] Add PV MSR to enable asynchronous page faults
 delivery.

On Thu, Oct 07, 2010 at 02:42:06PM +0200, Avi Kivity wrote:
>  On 10/04/2010 05:56 PM, Gleb Natapov wrote:
> >Guest enables async PF vcpu functionality using this MSR.
> >
> >  			return NON_PRESENT;
> >+
> >+MSR_KVM_ASYNC_PF_EN: 0x4b564d02
> >+	data: Bits 63-6 hold 64-byte aligned physical address of a 32bit memory
> 
> Given that it must be aligned anyway, we can require it to be a
> 64-byte region and also require that the guest zero it before
> writing the MSR.  That will give us a little more flexibility in the
> future.
> 
No code change needed, so OK.

> >+	area which must be in guest RAM. Bits 5-1 are reserved and should be
> >+	zero. Bit 0 is 1 when asynchronous page faults are enabled on the vcpu
> >+	0 when disabled.
> >+
> >+	Physical address points to 32 bit memory location that will be written
> >+	to by the hypervisor at the time of asynchronous page fault injection to
> >+	indicate type of asynchronous page fault. Value of 1 means that the page
> >+	referred to by the page fault is not present. Value 2 means that the
> >+	page is now available.
> >diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >index b9f263e..de31551 100644
> >--- a/arch/x86/include/asm/kvm_host.h
> >+++ b/arch/x86/include/asm/kvm_host.h
> >@@ -417,6 +417,8 @@ struct kvm_vcpu_arch {
> >
> >  	struct {
> >  		gfn_t gfns[roundup_pow_of_two(ASYNC_PF_PER_VCPU)];
> >+		struct gfn_to_hva_cache data;
> >+		u64 msr_val;
> >  	} apf;
> >  };
> >
> >diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> >index e3faaaf..8662ae0 100644
> >--- a/arch/x86/include/asm/kvm_para.h
> >+++ b/arch/x86/include/asm/kvm_para.h
> >@@ -20,6 +20,7 @@
> >   * are available. The use of 0x11 and 0x12 is deprecated
> >   */
> >  #define KVM_FEATURE_CLOCKSOURCE2        3
> >+#define KVM_FEATURE_ASYNC_PF		4
> >
> >  /* The last 8 bits are used to indicate how to interpret the flags field
> >   * in pvclock structure. If no bits are set, all flags are ignored.
> >@@ -32,9 +33,12 @@
> >  /* Custom MSRs falls in the range 0x4b564d00-0x4b564dff */
> >  #define MSR_KVM_WALL_CLOCK_NEW  0x4b564d00
> >  #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
> >+#define MSR_KVM_ASYNC_PF_EN 0x4b564d02
> >
> >  #define KVM_MAX_MMU_OP_BATCH           32
> >
> >+#define KVM_ASYNC_PF_ENABLED			(1<<  0)
> >+
> >  /* Operations for KVM_HC_MMU_OP */
> >  #define KVM_MMU_OP_WRITE_PTE            1
> >  #define KVM_MMU_OP_FLUSH_TLB	        2
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index 48fd59d..3e123ab 100644
> >--- a/arch/x86/kvm/x86.c
> >+++ b/arch/x86/kvm/x86.c
> >@@ -782,12 +782,12 @@ EXPORT_SYMBOL_GPL(kvm_get_dr);
> >   * kvm-specific. Those are put in the beginning of the list.
> >   */
> >
> >-#define KVM_SAVE_MSRS_BEGIN	7
> >+#define KVM_SAVE_MSRS_BEGIN	8
> >  static u32 msrs_to_save[] = {
> >  	MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
> >  	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
> >  	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
> >-	HV_X64_MSR_APIC_ASSIST_PAGE,
> >+	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN,
> >  	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
> >  	MSR_STAR,
> >  #ifdef CONFIG_X86_64
> >@@ -1425,6 +1425,29 @@ static int set_msr_hyperv(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> >  	return 0;
> >  }
> >
> >+static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
> >+{
> >+	gpa_t gpa = data&  ~0x3f;
> >+
> >+	/* Bits 1:5 are resrved, Should be zero */
> >+	if (data&  0x3e)
> >+		return 1;
> >+
> >+	vcpu->arch.apf.msr_val = data;
> >+
> >+	if (!(data&  KVM_ASYNC_PF_ENABLED)) {
> >+		kvm_clear_async_pf_completion_queue(vcpu);
> 
> May be a lengthy synchronous operation.  I guess we don't care.
> 
> >+		memset(vcpu->arch.apf.gfns, 0xff, sizeof vcpu->arch.apf.gfns);
> 
> That memset again.
> 
> >+		return 0;
> >+	}
> >+
> >+	if (kvm_gfn_to_hva_cache_init(vcpu->kvm,&vcpu->arch.apf.data, gpa))
> >+		return 1;
> 
> Note: we need to handle the memory being removed from underneath
> kvm_gfn_to_hve_cache().  Given that, we can just make
> kvm_gfn_to_hva_cache_init() return void.  "success" means nothing
> when future changes can invalidate it.
> 
I want to catch guest doing stupid things. If guest give us non-existent
address I want wrmsr to #GP.

> >+
> >+	kvm_async_pf_wakeup_all(vcpu);
> 
> Why is this needed?  If all apfs are flushed at disable time, what
> do we need to wake up?
For migration. Destination will rewrite msr and all processes will be
waked up.

> 
> Need to list the MSR for save/restore/reset.
> 
> 
This patch adds it to msrs_to_save, no?

--
			Gleb.
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