[MODERATED] Re: [PATCH v5 6/8] NX 6

Kanth Ghatraju <[email protected]> Wed, 9 Oct 2019 19:03:10 -0400

Newsgroups	org.kernel.lore.historical-speck
Message-ID	<[email protected]>

Hi Ben,


A couple of options:

1. You could revert 6ca18b6950f8dee29361722f28f69847724b276f with commit 7390de1e99a70895721165d0ccd4a6e16482960a
2. Use kvm_mmu_invalidate_zap_all_pages()

-kanth

> On Oct 9, 2019, at 6:42 PM, speck for Ben Hutchings <[email protected]> wrote:
> 
> On Mon, 2019-07-01 at 15:52 +0200, speck for Paolo Bonzini wrote:
>> From: Paolo Bonzini <[email protected]>
>> Subject: [PATCH 6/8] kvm: mmu: ITLB_MULTIHIT mitigation
> [...]
>> +static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
>> +{
>> +	bool old_val = nx_huge_pages;
>> +	bool new_val;
>> +
>> +	/* In "auto" mode deploy workaround only if CPU has the bug. */
>> +	if (sysfs_streq(val, "off"))
>> +		new_val = 0;
>> +	else if (sysfs_streq(val, "force"))
>> +		new_val = 1;
>> +	else if (sysfs_streq(val, "auto"))
>> +		new_val = boot_cpu_has_bug(X86_BUG_ITLB_MULTIHIT);
>> +	else if (strtobool(val, &new_val) < 0)
>> +		return -EINVAL;
>> +
>> +	__set_nx_huge_pages(new_val);
>> +
>> +	if (new_val != old_val) {
>> +		struct kvm *kvm;
>> +		int idx;
>> +
>> +		mutex_lock(&kvm_lock);
>> +
>> +		list_for_each_entry(kvm, &vm_list, vm_list) {
>> +			idx = srcu_read_lock(&kvm->srcu);
>> +			kvm_mmu_zap_all(kvm);
>> +			srcu_read_unlock(&kvm->srcu, idx);
>> +		}
>> +		mutex_unlock(&kvm_lock);
>> +	}
> [...]
> 
> I've started trying to backport the NX patches to stable branches, and
> I think I can take them back as far as 4.9.
> 
> However, kvm_mmu_zap_all() is a relatively new addition and looks hard
> to backport.  I intend to make the nx_huge_pages parameter read-only
> (0444 permissions) and delete this "if (new_val != old_val)" block.
> Does that seem reasonable?
> 
> Ben.
> 
> --
> Ben Hutchings
> Humans are not rational beings; they are rationalising beings.
>

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