linux-kernel - Re: [PATCH] KVM: x86/mmu: improve robustness of some functions

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Date:   Mon, 25 Jan 2021 10:54:18 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Stephen Zhang <stephenzhangzsd@...il.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stephen Zhang <stephenzhangzsd@...il.com>, pbonzini@...hat.com,
        seanjc@...gle.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com
Subject: Re: [PATCH] KVM: x86/mmu: improve robustness of some functions

Stephen Zhang <stephenzhangzsd@...il.com> writes:

> If the name of this function changes, you can easily
> forget to modify the code in the corresponding place.
> In fact, such errors already exist in spte_write_protect
>  and spte_clear_dirty.
>

What if we do something like (completely untested):

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index bfc6389edc28..5ec15e4160b1 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -12,7 +12,7 @@
 extern bool dbg;
 
 #define pgprintk(x...) do { if (dbg) printk(x); } while (0)
-#define rmap_printk(x...) do { if (dbg) printk(x); } while (0)
+#define rmap_printk(fmt, args...) do { if (dbg) printk("%s: " fmt, __func__, ## args); } while (0)
 #define MMU_WARN_ON(x) WARN_ON(x)
 #else
 #define pgprintk(x...) do { } while (0)

and eliminate the need to pass '__func__,' explicitly? We can probably
do the same to pgprintk().

> Signed-off-by: Stephen Zhang <stephenzhangzsd@...il.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 6d16481..09462c3d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -844,17 +844,17 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
>  	int i, count = 0;
>  
>  	if (!rmap_head->val) {
> -		rmap_printk("pte_list_add: %p %llx 0->1\n", spte, *spte);
> +		rmap_printk("%s: %p %llx 0->1\n", __func__, spte, *spte);
>  		rmap_head->val = (unsigned long)spte;
>  	} else if (!(rmap_head->val & 1)) {
> -		rmap_printk("pte_list_add: %p %llx 1->many\n", spte, *spte);
> +		rmap_printk("%s: %p %llx 1->many\n", __func__, spte, *spte);
>  		desc = mmu_alloc_pte_list_desc(vcpu);
>  		desc->sptes[0] = (u64 *)rmap_head->val;
>  		desc->sptes[1] = spte;
>  		rmap_head->val = (unsigned long)desc | 1;
>  		++count;
>  	} else {
> -		rmap_printk("pte_list_add: %p %llx many->many\n", spte, *spte);
> +		rmap_printk("%s: %p %llx many->many\n",	__func__, spte, *spte);
>  		desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
>  		while (desc->sptes[PTE_LIST_EXT-1]) {
>  			count += PTE_LIST_EXT;
> @@ -1115,7 +1115,7 @@ static bool spte_write_protect(u64 *sptep, bool pt_protect)
>  	      !(pt_protect && spte_can_locklessly_be_made_writable(spte)))
>  		return false;
>  
> -	rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
> +	rmap_printk("%s: spte %p %llx\n", __func__, sptep, *sptep);
>  
>  	if (pt_protect)
>  		spte &= ~SPTE_MMU_WRITEABLE;
> @@ -1142,7 +1142,7 @@ static bool spte_clear_dirty(u64 *sptep)
>  {
>  	u64 spte = *sptep;
>  
> -	rmap_printk("rmap_clear_dirty: spte %p %llx\n", sptep, *sptep);
> +	rmap_printk("%s: spte %p %llx\n", __func__, sptep, *sptep);
>  
>  	MMU_WARN_ON(!spte_ad_enabled(spte));
>  	spte &= ~shadow_dirty_mask;
> @@ -1184,7 +1184,7 @@ static bool spte_set_dirty(u64 *sptep)
>  {
>  	u64 spte = *sptep;
>  
> -	rmap_printk("rmap_set_dirty: spte %p %llx\n", sptep, *sptep);
> +	rmap_printk("%s: spte %p %llx\n", __func__, sptep, *sptep);
>  
>  	/*
>  	 * Similar to the !kvm_x86_ops.slot_disable_log_dirty case,
> @@ -1363,8 +1363,8 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
>  
>  restart:
>  	for_each_rmap_spte(rmap_head, &iter, sptep) {
> -		rmap_printk("kvm_set_pte_rmapp: spte %p %llx gfn %llx (%d)\n",
> -			    sptep, *sptep, gfn, level);
> +		rmap_printk("%s: spte %p %llx gfn %llx (%d)\n",
> +			      __func__, sptep, *sptep, gfn, level);
>  
>  		need_flush = 1;

-- 
Vitaly