Commit 350c49fd authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Delete rmap_printk() and all its usage 

Delete rmap_printk() so that MMU_WARN_ON() and MMU_DEBUG can be morphed
into something that can be regularly enabled for debug kernels.  The
information provided by rmap_printk() isn't all that useful now that the
rmap and unsync code is mature, as the prints are simultaneously too
verbose (_lots_ of message) and yet not verbose enough to be helpful for
debug (most instances print just the SPTE pointer/value, which is rarely
sufficient to root cause anything but trivial bugs).

Alternatively, rmap_printk() could be reworked to into tracepoints, but
it's not clear there is a real need as rmap bugs rarely escape initial
development, and when bugs do escape to production, they are often edge
cases and/or reside in code that isn't directly related to the rmaps.
In other words, the problems with rmap_printk() being unhelpful also apply
to tracepoints.  And deleting rmap_printk() doesn't preclude adding
tracepoints in the future.

Link: https://lore.kernel.org/r/20230729004722.1056172-3-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a98b8894

arch/x86/kvm/mmu/mmu.c

+0 −12
Original line number Diff line number Diff line
@@ -937,10 +937,8 @@ static int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte, 
	int count = 0;



	if (!rmap_head->val) {

		rmap_printk("%p %llx 0->1\n", spte, *spte);

		rmap_head->val = (unsigned long)spte;

	} else if (!(rmap_head->val & 1)) {

		rmap_printk("%p %llx 1->many\n", spte, *spte);

		desc = kvm_mmu_memory_cache_alloc(cache);

		desc->sptes[0] = (u64 *)rmap_head->val;

		desc->sptes[1] = spte;
@@ -949,7 +947,6 @@ static int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte, 
		rmap_head->val = (unsigned long)desc | 1;

		++count;

	} else {

		rmap_printk("%p %llx many->many\n", spte, *spte);

		desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);

		count = desc->tail_count + desc->spte_count;
@@ -1014,14 +1011,12 @@ static void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head) 
		pr_err("%s: %p 0->BUG\n", __func__, spte);

		BUG();

	} else if (!(rmap_head->val & 1)) {

		rmap_printk("%p 1->0\n", spte);

		if ((u64 *)rmap_head->val != spte) {

			pr_err("%s:  %p 1->BUG\n", __func__, spte);

			BUG();

		}

		rmap_head->val = 0;

	} else {

		rmap_printk("%p many->many\n", spte);

		desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);

		while (desc) {

			for (i = 0; i < desc->spte_count; ++i) {
@@ -1237,8 +1232,6 @@ static bool spte_write_protect(u64 *sptep, bool pt_protect) 
	    !(pt_protect && is_mmu_writable_spte(spte)))

		return false;



	rmap_printk("spte %p %llx\n", sptep, *sptep);



	if (pt_protect)

		spte &= ~shadow_mmu_writable_mask;

	spte = spte & ~PT_WRITABLE_MASK;
@@ -1263,8 +1256,6 @@ static bool spte_clear_dirty(u64 *sptep) 
{

	u64 spte = *sptep;



	rmap_printk("spte %p %llx\n", sptep, *sptep);



	MMU_WARN_ON(!spte_ad_enabled(spte));

	spte &= ~shadow_dirty_mask;

	return mmu_spte_update(sptep, spte);
@@ -1476,9 +1467,6 @@ static bool kvm_set_pte_rmap(struct kvm *kvm, struct kvm_rmap_head *rmap_head, 


restart:

	for_each_rmap_spte(rmap_head, &iter, sptep) {

		rmap_printk("spte %p %llx gfn %llx (%d)\n",

			    sptep, *sptep, gfn, level);



		need_flush = true;



		if (pte_write(pte)) {

arch/x86/kvm/mmu/mmu_internal.h

+0 −2
Original line number Diff line number Diff line
@@ -11,10 +11,8 @@ 
#ifdef MMU_DEBUG

extern bool dbg;



#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 rmap_printk(x...) do { } while (0)

#define MMU_WARN_ON(x) do { } while (0)

#endif