Re: [PATCH 2/3] add SPTE_HOST_WRITEABLE flag to the shadow ptes

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Sep 10, 2009 at 07:38:57PM +0300, Izik Eidus wrote:
> this flag notify that the host physical page we are pointing to from
> the spte is write protected, and therefore we cant change its access
> to be write unless we run get_user_pages(write = 1).
> 
> (this is needed for change_pte support in kvm)
> 
> Signed-off-by: Izik Eidus <ieidus@redhat.com>
> ---
>  arch/x86/kvm/mmu.c         |   15 +++++++++++----
>  arch/x86/kvm/paging_tmpl.h |   18 +++++++++++++++---
>  2 files changed, 26 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 62d2f86..a7151b8 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -156,6 +156,8 @@ module_param(oos_shadow, bool, 0644);
>  #define CREATE_TRACE_POINTS
>  #include "mmutrace.h"
>  
> +#define SPTE_HOST_WRITEABLE (1ULL << PT_FIRST_AVAIL_BITS_SHIFT)
> +
>  #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
>  
>  struct kvm_rmap_desc {
> @@ -1754,7 +1756,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  		    unsigned pte_access, int user_fault,
>  		    int write_fault, int dirty, int level,
>  		    gfn_t gfn, pfn_t pfn, bool speculative,
> -		    bool can_unsync)
> +		    bool can_unsync, bool reset_host_protection)
				     bool host_pte_writeable ?

>  {
>  	u64 spte;
>  	int ret = 0;
> @@ -1781,6 +1783,9 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  		spte |= kvm_x86_ops->get_mt_mask(vcpu, gfn,
>  			kvm_is_mmio_pfn(pfn));
>  
> +	if (reset_host_protection)
> +		spte |= SPTE_HOST_WRITEABLE;
> +
>  	spte |= (u64)pfn << PAGE_SHIFT;
>  
>  	if ((pte_access & ACC_WRITE_MASK)
> @@ -1826,7 +1831,8 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  			 unsigned pt_access, unsigned pte_access,
>  			 int user_fault, int write_fault, int dirty,
>  			 int *ptwrite, int level, gfn_t gfn,
> -			 pfn_t pfn, bool speculative)
> +			 pfn_t pfn, bool speculative,
> +			 bool reset_host_protection)
>  {
>  	int was_rmapped = 0;
>  	int was_writeble = is_writeble_pte(*sptep);
> @@ -1858,7 +1864,8 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  	}
>  
>  	if (set_spte(vcpu, sptep, pte_access, user_fault, write_fault,
> -		      dirty, level, gfn, pfn, speculative, true)) {
> +		      dirty, level, gfn, pfn, speculative, true,
> +		      reset_host_protection)) {
>  		if (write_fault)
>  			*ptwrite = 1;
>  		kvm_x86_ops->tlb_flush(vcpu);
> @@ -1906,7 +1913,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
>  		if (iterator.level == level) {
>  			mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, ACC_ALL,
>  				     0, write, 1, &pt_write,
> -				     level, gfn, pfn, false);
> +				     level, gfn, pfn, false, true);
>  			++vcpu->stat.pf_fixed;
>  			break;
>  		}
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index d2fec9c..c9256ee 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -273,9 +273,13 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
>  	if (mmu_notifier_retry(vcpu, vcpu->arch.update_pte.mmu_seq))
>  		return;
>  	kvm_get_pfn(pfn);
> + 	/*
> + 	 * we call mmu_set_spte() with reset_host_protection = true beacuse that
> + 	 * vcpu->arch.update_pte.pfn was fetched from get_user_pages(write = 1).
> + 	 */
>  	mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
>  		     gpte & PT_DIRTY_MASK, NULL, PT_PAGE_TABLE_LEVEL,
> -		     gpte_to_gfn(gpte), pfn, true);
> +		     gpte_to_gfn(gpte), pfn, true, true);
>  }
>  
>  /*
> @@ -308,7 +312,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
>  				     user_fault, write_fault,
>  				     gw->ptes[gw->level-1] & PT_DIRTY_MASK,
>  				     ptwrite, level,
> -				     gw->gfn, pfn, false);
> +				     gw->gfn, pfn, false, true);
>  			break;
>  		}
>  
> @@ -558,6 +562,7 @@ static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
>  static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>  {
>  	int i, offset, nr_present;
> +        bool reset_host_protection;

Tab damaged.

>  	offset = nr_present = 0;
>  
> @@ -595,9 +600,16 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>  
>  		nr_present++;
>  		pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
> +		if (!(sp->spt[i] & SPTE_HOST_WRITEABLE)) {
> + 			pte_access &= ~PT_WRITABLE_MASK;
> +			reset_host_protection = 0;
> +		} else {
> +			reset_host_protection = 1;
> +		}
>  		set_spte(vcpu, &sp->spt[i], pte_access, 0, 0,
>  			 is_dirty_gpte(gpte), PT_PAGE_TABLE_LEVEL, gfn,
> -			 spte_to_pfn(sp->spt[i]), true, false);
> +			 spte_to_pfn(sp->spt[i]), true, false,
> +			 reset_host_protection);
>  	}
>  
>  	return !nr_present;

Looks good otherwise.

> -- 
> 1.5.6.5
> 
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