| Message ID | 20220913085452.25561-1-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/mmu: use helper macro SPTE_ENT_PER_PAGE | expand |
On Tue, Sep 13, 2022, Miaohe Lin wrote: > Use helper macro SPTE_ENT_PER_PAGE to get the number of spte entries > per page. Minor readability improvement. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- Reviewed-by: Sean Christopherson <seanjc@google.com> > arch/x86/kvm/mmu/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 858bc53cfab4..45c532d00f78 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -1645,7 +1645,7 @@ static int is_empty_shadow_page(u64 *spt) > u64 *pos; > u64 *end; > > - for (pos = spt, end = pos + PAGE_SIZE / sizeof(u64); pos != end; pos++) > + for (pos = spt, end = pos + SPTE_ENT_PER_PAGE; pos != end; pos++) This is buried under MMU_DEBUG, and turning that on to compile test, which requires manually changing kernel code to enable, results in some minor warnings. Given the existence of CONFIG_KVM_WERROR=y, I think it's safe to say this code hasn't been exercised in a very long time. E.g. this is literally the first time I've actually enabled MMU_DEBUG. This particular check seems like it would be quite useful, but the pgprintk() and rmap_printk() hooks, not so much. E.g. the knob is too coarse grained, and many of the prints now have tracepoints. So, unless someone actually actively uses MMU_DEBUG+dbg, I'm inclined to just delete pgprintk() and rmap_printk(), and then rename MMU_WARN_ON => KVM_MMU_WARN_ON and add a Kconfig for that, e.g. CONFIG_KVM_PROVE_MMU. Hmm, and maybe clean up this helper too, e.g. get rid of the pointer arithmetic, and take the full kvm_mmu_page so that the error message can print out things like the gfn (a host kernel pointer is going to be useless for debug). Thoughts? Objections?
On 2022/10/6 7:17, Sean Christopherson wrote: > On Tue, Sep 13, 2022, Miaohe Lin wrote: >> Use helper macro SPTE_ENT_PER_PAGE to get the number of spte entries >> per page. Minor readability improvement. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- > > Reviewed-by: Sean Christopherson <seanjc@google.com> Many thanks for your review and comment. And sorry for late respond. A really busy week. :) > >> arch/x86/kvm/mmu/mmu.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c >> index 858bc53cfab4..45c532d00f78 100644 >> --- a/arch/x86/kvm/mmu/mmu.c >> +++ b/arch/x86/kvm/mmu/mmu.c >> @@ -1645,7 +1645,7 @@ static int is_empty_shadow_page(u64 *spt) >> u64 *pos; >> u64 *end; >> >> - for (pos = spt, end = pos + PAGE_SIZE / sizeof(u64); pos != end; pos++) >> + for (pos = spt, end = pos + SPTE_ENT_PER_PAGE; pos != end; pos++) > > This is buried under MMU_DEBUG, and turning that on to compile test, which requires > manually changing kernel code to enable, results in some minor warnings. Given the > existence of CONFIG_KVM_WERROR=y, I think it's safe to say this code hasn't been > exercised in a very long time. E.g. this is literally the first time I've actually > enabled MMU_DEBUG. > > This particular check seems like it would be quite useful, but the pgprintk() and > rmap_printk() hooks, not so much. E.g. the knob is too coarse grained, and many > of the prints now have tracepoints. > > So, unless someone actually actively uses MMU_DEBUG+dbg, I'm inclined to just delete > pgprintk() and rmap_printk(), and then rename MMU_WARN_ON => KVM_MMU_WARN_ON and > add a Kconfig for that, e.g. CONFIG_KVM_PROVE_MMU. > > Hmm, and maybe clean up this helper too, e.g. get rid of the pointer arithmetic, > and take the full kvm_mmu_page so that the error message can print out things like > the gfn (a host kernel pointer is going to be useless for debug). > > Thoughts? Objections? I tend to agree with you. MMU_DEBUG might even be an obsolete DEBUG component. I believe above changes will improve the current code. Am I supposed to do this or will you kindly do this? Thanks again, Miaohe Lin
Queued, thanks. Paolo
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 858bc53cfab4..45c532d00f78 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1645,7 +1645,7 @@ static int is_empty_shadow_page(u64 *spt) u64 *pos; u64 *end; - for (pos = spt, end = pos + PAGE_SIZE / sizeof(u64); pos != end; pos++) + for (pos = spt, end = pos + SPTE_ENT_PER_PAGE; pos != end; pos++) if (is_shadow_present_pte(*pos)) { printk(KERN_ERR "%s: %p %llx\n", __func__, pos, *pos);
Use helper macro SPTE_ENT_PER_PAGE to get the number of spte entries per page. Minor readability improvement. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- arch/x86/kvm/mmu/mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)