Re: [Xen-devel] [PATCH v3 1/2] x86/mm: Clean IOMMU flags from p2m-pt code

[Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>]

Hi George,

Did you get a chance to look at this clean-up?

Thanks,
Alex

On 16.07.2019 15:01, Alexandru Stefan ISAILA wrote:
> At this moment IOMMU pt sharing is disabled by commit [1].
> 
> This patch aims to clear the IOMMU hap share support as it will not be
> used in the future. By doing this the IOMMU bits used in pte[52:58] can
> be used in other ways.
> 
> [1] c2ba3db31ef2d9f1e40e7b6c16cf3be3d671d555
> 
> Suggested-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> 
> ---
> Changes since V1:
>       - Rework commit message
>       - Reflow comments
>       - Move flags init to declaration in p2m_type_to_flags.
> ---
>   xen/arch/x86/mm/p2m-pt.c | 96 +++-------------------------------------
>   1 file changed, 5 insertions(+), 91 deletions(-)
> 
> diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
> index cafc9f299b..3a0a500d66 100644
> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -24,7 +24,6 @@
>    * along with this program; If not, see <http://www.gnu.org/licenses/>.
>    */
>   
> -#include <xen/iommu.h>
>   #include <xen/vm_event.h>
>   #include <xen/event.h>
>   #include <xen/trace.h>
> @@ -36,15 +35,13 @@
>   #include <asm/p2m.h>
>   #include <asm/mem_sharing.h>
>   #include <asm/hvm/nestedhvm.h>
> -#include <asm/hvm/svm/amd-iommu-proto.h>
>   
>   #include "mm-locks.h"
>   
>   /*
>    * We may store INVALID_MFN in PTEs.  We need to clip this to avoid 
> trampling
> - * over higher-order bits (NX, p2m type, IOMMU flags).  We seem to not need
> - * to unclip on the read path, as callers are concerned only with p2m type in
> - * such cases.
> + * over higher-order bits (NX, p2m type). We seem to not need to unclip on 
> the
> + * read path, as callers are concerned only with p2m type in such cases.
>    */
>   #define p2m_l1e_from_pfn(pfn, flags)    \
>       l1e_from_pfn((pfn) & (PADDR_MASK >> PAGE_SHIFT), (flags))
> @@ -71,13 +68,7 @@ static unsigned long p2m_type_to_flags(const struct 
> p2m_domain *p2m,
>                                          mfn_t mfn,
>                                          unsigned int level)
>   {
> -    unsigned long flags;
> -    /*
> -     * AMD IOMMU: When we share p2m table with iommu, bit 9 - bit 11 will be
> -     * used for iommu hardware to encode next io page level. Bit 59 - bit 62
> -     * are used for iommu flags, We could not use these bits to store p2m 
> types.
> -     */
> -    flags = (unsigned long)(t & 0x7f) << 12;
> +    unsigned long flags = (unsigned long)(t & 0x7f) << 12;
>   
>       switch(t)
>       {
> @@ -165,16 +156,6 @@ p2m_free_entry(struct p2m_domain *p2m, l1_pgentry_t 
> *p2m_entry, int page_order)
>   // Returns 0 on error.
>   //
>   
> -/* AMD IOMMU: Convert next level bits and r/w bits into 24 bits p2m flags */
> -#define iommu_nlevel_to_flags(nl, f) ((((nl) & 0x7) << 9 )|(((f) & 0x3) << 
> 21))
> -
> -static void p2m_add_iommu_flags(l1_pgentry_t *p2m_entry,
> -                                unsigned int nlevel, unsigned int flags)
> -{
> -    if ( iommu_hap_pt_share )
> -        l1e_add_flags(*p2m_entry, iommu_nlevel_to_flags(nlevel, flags));
> -}
> -
>   /* Returns: 0 for success, -errno for failure */
>   static int
>   p2m_next_level(struct p2m_domain *p2m, void **table,
> @@ -203,7 +184,6 @@ p2m_next_level(struct p2m_domain *p2m, void **table,
>   
>           new_entry = l1e_from_mfn(mfn, P2M_BASE_FLAGS | _PAGE_RW);
>   
> -        p2m_add_iommu_flags(&new_entry, level, 
> IOMMUF_readable|IOMMUF_writable);
>           rc = p2m->write_p2m_entry(p2m, gfn, p2m_entry, new_entry, level + 
> 1);
>           if ( rc )
>               goto error;
> @@ -242,13 +222,6 @@ p2m_next_level(struct p2m_domain *p2m, void **table,
>   
>           l1_entry = map_domain_page(mfn);
>   
> -        /* Inherit original IOMMU permissions, but update Next Level. */
> -        if ( iommu_hap_pt_share )
> -        {
> -            flags &= ~iommu_nlevel_to_flags(~0, 0);
> -            flags |= iommu_nlevel_to_flags(level - 1, 0);
> -        }
> -
>           for ( i = 0; i < (1u << PAGETABLE_ORDER); i++ )
>           {
>               new_entry = l1e_from_pfn(pfn | (i << ((level - 1) * 
> PAGETABLE_ORDER)),
> @@ -264,8 +237,6 @@ p2m_next_level(struct p2m_domain *p2m, void **table,
>           unmap_domain_page(l1_entry);
>   
>           new_entry = l1e_from_mfn(mfn, P2M_BASE_FLAGS | _PAGE_RW);
> -        p2m_add_iommu_flags(&new_entry, level,
> -                            IOMMUF_readable|IOMMUF_writable);
>           rc = p2m->write_p2m_entry(p2m, gfn, p2m_entry, new_entry,
>                                     level + 1);
>           if ( rc )
> @@ -470,9 +441,6 @@ static int do_recalc(struct p2m_domain *p2m, unsigned 
> long gfn)
>               }
>   
>               e = l1e_from_pfn(mfn, flags);
> -            p2m_add_iommu_flags(&e, level,
> -                                (nt == p2m_ram_rw)
> -                                ? IOMMUF_readable|IOMMUF_writable : 0);
>               ASSERT(!needs_recalc(l1, e));
>           }
>           else
> @@ -540,18 +508,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>       l2_pgentry_t l2e_content;
>       l3_pgentry_t l3e_content;
>       int rc;
> -    unsigned int iommu_pte_flags = p2m_get_iommu_flags(p2mt, mfn);
> -    /*
> -     * old_mfn and iommu_old_flags control possible flush/update needs on the
> -     * IOMMU: We need to flush when MFN or flags (i.e. permissions) change.
> -     * iommu_old_flags being initialized to zero covers the case of the entry
> -     * getting replaced being a non-present (leaf or intermediate) one. For
> -     * present leaf entries the real value will get calculated below, while
> -     * for present intermediate entries ~0 (guaranteed != iommu_pte_flags)
> -     * will be used (to cover all cases of what the leaf entries underneath
> -     * the intermediate one might be).
> -     */
> -    unsigned int flags, iommu_old_flags = 0;
> +    unsigned int flags;
>       unsigned long old_mfn = mfn_x(INVALID_MFN);
>   
>       if ( !sve )
> @@ -599,17 +556,9 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>           if ( flags & _PAGE_PRESENT )
>           {
>               if ( flags & _PAGE_PSE )
> -            {
>                   old_mfn = l1e_get_pfn(*p2m_entry);
> -                iommu_old_flags =
> -                    p2m_get_iommu_flags(p2m_flags_to_type(flags),
> -                                        _mfn(old_mfn));
> -            }
>               else
> -            {
> -                iommu_old_flags = ~0;
>                   intermediate_entry = *p2m_entry;
> -            }
>           }
>   
>           check_entry(mfn, p2mt, p2m_flags_to_type(flags), page_order);
> @@ -619,9 +568,6 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>               : l3e_empty();
>           entry_content.l1 = l3e_content.l3;
>   
> -        if ( entry_content.l1 != 0 )
> -            p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
> -
>           rc = p2m->write_p2m_entry(p2m, gfn, p2m_entry, entry_content, 3);
>           /* NB: paging_write_p2m_entry() handles tlb flushes properly */
>           if ( rc )
> @@ -648,9 +594,6 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>                                      0, L1_PAGETABLE_ENTRIES);
>           ASSERT(p2m_entry);
>           old_mfn = l1e_get_pfn(*p2m_entry);
> -        iommu_old_flags =
> -            p2m_get_iommu_flags(p2m_flags_to_type(l1e_get_flags(*p2m_entry)),
> -                                _mfn(old_mfn));
>   
>           if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
>               entry_content = p2m_l1e_from_pfn(mfn_x(mfn),
> @@ -658,9 +601,6 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>           else
>               entry_content = l1e_empty();
>   
> -        if ( entry_content.l1 != 0 )
> -            p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
> -
>           /* level 1 entry */
>           rc = p2m->write_p2m_entry(p2m, gfn, p2m_entry, entry_content, 1);
>           /* NB: paging_write_p2m_entry() handles tlb flushes properly */
> @@ -677,17 +617,9 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>           if ( flags & _PAGE_PRESENT )
>           {
>               if ( flags & _PAGE_PSE )
> -            {
>                   old_mfn = l1e_get_pfn(*p2m_entry);
> -                iommu_old_flags =
> -                    p2m_get_iommu_flags(p2m_flags_to_type(flags),
> -                                        _mfn(old_mfn));
> -            }
>               else
> -            {
> -                iommu_old_flags = ~0;
>                   intermediate_entry = *p2m_entry;
> -            }
>           }
>   
>           check_entry(mfn, p2mt, p2m_flags_to_type(flags), page_order);
> @@ -697,9 +629,6 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>               : l2e_empty();
>           entry_content.l1 = l2e_content.l2;
>   
> -        if ( entry_content.l1 != 0 )
> -            p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
> -
>           rc = p2m->write_p2m_entry(p2m, gfn, p2m_entry, entry_content, 2);
>           /* NB: paging_write_p2m_entry() handles tlb flushes properly */
>           if ( rc )
> @@ -711,24 +640,9 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>            && (gfn + (1UL << page_order) - 1 > p2m->max_mapped_pfn) )
>           p2m->max_mapped_pfn = gfn + (1UL << page_order) - 1;
>   
> -    if ( iommu_enabled && (iommu_old_flags != iommu_pte_flags ||
> -                           old_mfn != mfn_x(mfn)) )
> -    {
> -        ASSERT(rc == 0);
> -
> -        if ( need_iommu_pt_sync(p2m->domain) )
> -            rc = iommu_pte_flags ?
> -                iommu_legacy_map(d, _dfn(gfn), mfn, page_order,
> -                                 iommu_pte_flags) :
> -                iommu_legacy_unmap(d, _dfn(gfn), page_order);
> -        else if ( iommu_use_hap_pt(d) && iommu_old_flags )
> -            amd_iommu_flush_pages(p2m->domain, gfn, page_order);
> -    }
> -
>       /*
>        * Free old intermediate tables if necessary.  This has to be the
> -     * last thing we do, after removal from the IOMMU tables, so as to
> -     * avoid a potential use-after-free.
> +     * last thing we do so as to avoid a potential use-after-free.
>        */
>       if ( l1e_get_flags(intermediate_entry) & _PAGE_PRESENT )
>           p2m_free_entry(p2m, &intermediate_entry, page_order);
> 
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