linux-kernel - Re: [PATCH 0/9] KVM: MTRR fixes and some cleanups

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Date:	Thu, 07 May 2015 18:53:31 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	guangrong.xiao@...ux.intel.com
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9] KVM: MTRR fixes and some cleanups



On 30/04/2015 12:24, guangrong.xiao@...ux.intel.com wrote:
> From: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> 
> This are some MTRR bugs if legacy IOMMU device is used on Intel's CPU:
> - In current code, whenever guest MTRR registers are changed
>   kvm_mmu_reset_context is called to switch to the new root shadow page
>   table, however, it's useless since:
>   1) the cache type is not cached into shadow page's attribute so that the
>      original root shadow page will be reused
> 
>   2) the cache type is set on the last spte, that means we should sync the
>      last sptes when MTRR is changed
> 
>   We can fix it by dropping all the spte in the gfn range which is
>   being updated by MTRR
> 
> - some bugs are in get_mtrr_type();
>   1: bit 2 of mtrr_state->enabled is corresponding bit 11 of IA32_MTRR_DEF_TYPE
>      MSR which completely control MTRR's enablement that means other bits are
>      ignored if it is cleared
> 
>   2: the fixed MTRR ranges are controlled by bit 1 of mtrr_state->enabled (bit
>      10 of IA32_MTRR_DEF_TYPE)
>   
>   3: if MTRR is disabled, UC is applied to all of physical memory rather than
>      mtrr_state->def_type
> 
> - we need not to reset mmu once cache policy is changed since shadow page table
>   does not virtualize any cache policy
> 
> Also, these are some cleanups to make current MMU code more cleaner and help
> us fixing the bug more easier. 
> 
> Xiao Guangrong (9):
>   KVM: MMU: fix decoding cache type from MTRR
>   KVM: MMU: introduce slot_handle_level() and its helper
>   KVM: MMU: use slot_handle_level and its helper to clean up the code
>   KVM: MMU: introduce for_each_rmap_spte()
>   KVM: MMU: KVM: introduce for_each_slot_rmap
>   KVM: MMU: introduce kvm_zap_rmapp
>   KVM: MMU: introduce kvm_zap_gfn_range()
>   KVM: MMU: fix MTRR update
>   KVM: x86: do not reset mmu if CR0.CD and CR0.NW are changed
> 
>  arch/x86/include/asm/kvm_host.h |   2 +
>  arch/x86/kvm/mmu.c              | 407 ++++++++++++++++++++++------------------
>  arch/x86/kvm/mmu.h              |   1 +
>  arch/x86/kvm/mmu_audit.c        |   4 +-
>  arch/x86/kvm/svm.c              |   5 +
>  arch/x86/kvm/vmx.c              |  58 ++++++
>  arch/x86/kvm/x86.c              |   5 +-
>  7 files changed, 294 insertions(+), 188 deletions(-)
> 

Very nice cleanups.  I made a couple comments on the patch ordering and
the API of iterator macros, but the basic ideas are great.  I'm going to
apply patch 1, and do some testing with kvm_arch_has_noncoherent_dma
forced to return true.

Paolo
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