linux-kernel - Re: [Patch v3 0/7] Optimize clear dirty log

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Date:   Tue, 21 Mar 2023 14:38:22 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     pbonzini@...hat.com, bgardon@...gle.com, dmatlack@...gle.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch v3 0/7] Optimize clear dirty log

On Tue, Mar 21, 2023, Sean Christopherson wrote:
> It won't.  MMU_WARN_ON() is dead code without manual modification to define MMU_DEBUG.
> Part of the reason I used MMU_WARN_ON() was to remind myself to send a patch/series
> to overhaul MMU_WARN_ON[*].  My thought/hope is that a Kconfig will allow developers
> and testers to run with a pile of assertions and sanity checks without impacting
> the runtime overhead for production builds.
> 
> [*] https://lore.kernel.org/all/Yz4Qi7cn7TWTWQjj@google.com/

Ugh, I'm definitely sending that patch, MMU_DEBUG has bitrotted and broken the
build yet again.

arch/x86/kvm/mmu/mmu.c: In function ‘kvm_mmu_free_shadow_page’:
arch/x86/kvm/mmu/mmu.c:1738:15: error: implicit declaration of function ‘is_empty_shadow_page’; did you mean ‘to_shadow_page’? [-Werror=implicit-function-declaration]
 1738 |  MMU_WARN_ON(!is_empty_shadow_page(sp->spt));
      |               ^~~~~~~~~~~~~~~~~~~~
include/asm-generic/bug.h:110:25: note: in definition of macro ‘WARN_ON_ONCE’
  110 |  int __ret_warn_on = !!(condition);   \
      |                         ^~~~~~~~~
arch/x86/kvm/mmu/mmu.c:1738:2: note: in expansion of macro ‘MMU_WARN_ON’
 1738 |  MMU_WARN_ON(!is_empty_shadow_page(sp->spt));
      |  ^~~~~~~~~~~