From: Yan Zhao <[email protected]>
Currently intel_gvt_is_valid_gfn() is called in two places:
(1) shadowing guest GGTT entry
(2) shadowing guest PPGTT leaf entry,
which was introduced in commit cc753fbe1ac4
("drm/i915/gvt: validate gfn before set shadow page entry").
However, now it's not necessary to call this interface any more, because
a. GGTT partial write issue has been fixed by
commit bc0686ff5fad
("drm/i915/gvt: support inconsecutive partial gtt entry write")
commit 510fe10b6180
("drm/i915/gvt: fix a bug of partially write ggtt enties")
b. PPGTT resides in normal guest RAM and we only treat 8-byte writes
as valid page table writes. Any invalid GPA found is regarded as
an error, either due to guest misbehavior/attack or bug in host
shadow code.
So,rather than do GFN pre-checking and replace invalid GFNs with
scratch GFN and continue silently, just remove the pre-checking and
abort PPGTT shadowing on error detected.
c. GFN validity check is still performed in
intel_gvt_dma_map_guest_page() --> gvt_pin_guest_page().
It's more desirable to call VFIO interface to do both validity check
and mapping.
Calling intel_gvt_is_valid_gfn() to do GFN validity check from KVM side
while later mapping the GFN through VFIO interface is unnecessarily
fragile and confusing for unaware readers.
Signed-off-by: Yan Zhao <[email protected]>
[sean: remove now-unused local variables]
Signed-off-by: Sean Christopherson <[email protected]>
---
drivers/gpu/drm/i915/gvt/gtt.c | 36 +---------------------------------
1 file changed, 1 insertion(+), 35 deletions(-)
diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index 58b9b316ae46..f30922c55a0c 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -49,22 +49,6 @@
static bool enable_out_of_sync = false;
static int preallocated_oos_pages = 8192;
-static bool intel_gvt_is_valid_gfn(struct intel_vgpu *vgpu, unsigned long gfn)
-{
- struct kvm *kvm = vgpu->vfio_device.kvm;
- int idx;
- bool ret;
-
- if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, vgpu->status))
- return false;
-
- idx = srcu_read_lock(&kvm->srcu);
- ret = kvm_is_visible_gfn(kvm, gfn);
- srcu_read_unlock(&kvm->srcu, idx);
-
- return ret;
-}
-
/*
* validate a gm address and related range size,
* translate it to host gm address
@@ -1333,11 +1317,9 @@ static int ppgtt_populate_shadow_entry(struct intel_vgpu *vgpu,
static int ppgtt_populate_spt(struct intel_vgpu_ppgtt_spt *spt)
{
struct intel_vgpu *vgpu = spt->vgpu;
- struct intel_gvt *gvt = vgpu->gvt;
- const struct intel_gvt_gtt_pte_ops *ops = gvt->gtt.pte_ops;
struct intel_vgpu_ppgtt_spt *s;
struct intel_gvt_gtt_entry se, ge;
- unsigned long gfn, i;
+ unsigned long i;
int ret;
trace_spt_change(spt->vgpu->id, "born", spt,
@@ -1354,13 +1336,6 @@ static int ppgtt_populate_spt(struct intel_vgpu_ppgtt_spt *spt)
ppgtt_generate_shadow_entry(&se, s, &ge);
ppgtt_set_shadow_entry(spt, &se, i);
} else {
- gfn = ops->get_pfn(&ge);
- if (!intel_gvt_is_valid_gfn(vgpu, gfn)) {
- ops->set_pfn(&se, gvt->gtt.scratch_mfn);
- ppgtt_set_shadow_entry(spt, &se, i);
- continue;
- }
-
ret = ppgtt_populate_shadow_entry(vgpu, spt, i, &ge);
if (ret)
goto fail;
@@ -2335,14 +2310,6 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
m.val64 = e.val64;
m.type = e.type;
- /* one PTE update may be issued in multiple writes and the
- * first write may not construct a valid gfn
- */
- if (!intel_gvt_is_valid_gfn(vgpu, gfn)) {
- ops->set_pfn(&m, gvt->gtt.scratch_mfn);
- goto out;
- }
-
ret = intel_gvt_dma_map_guest_page(vgpu, gfn, PAGE_SIZE,
&dma_addr);
if (ret) {
@@ -2359,7 +2326,6 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
ops->clear_present(&m);
}
-out:
ggtt_set_guest_entry(ggtt_mm, &e, g_gtt_index);
ggtt_get_host_entry(ggtt_mm, &e, g_gtt_index);
--
2.40.1.606.ga4b1b128d6-goog
On 5/13/2023 8:35 AM, Sean Christopherson wrote:
> From: Yan Zhao <[email protected]>
>
Acked-by: Zhi Wang <[email protected]>
This was previously to avoid stepping down to the lower level ASAP
when a guest page is not used but still stays in the GPU page table.
(mostly in windows VM, as this is a behavior of WDDM GPU MM). But
it doesn't totally solve the the trapping flood in practice. I am
totally fine that it is removed. Post shadow in the trapping
path might be extended to handle this problem.
> Currently intel_gvt_is_valid_gfn() is called in two places:
> (1) shadowing guest GGTT entry
> (2) shadowing guest PPGTT leaf entry,
> which was introduced in commit cc753fbe1ac4
> ("drm/i915/gvt: validate gfn before set shadow page entry").
>
> However, now it's not necessary to call this interface any more, because
> a. GGTT partial write issue has been fixed by
> commit bc0686ff5fad
> ("drm/i915/gvt: support inconsecutive partial gtt entry write")
> commit 510fe10b6180
> ("drm/i915/gvt: fix a bug of partially write ggtt enties")
> b. PPGTT resides in normal guest RAM and we only treat 8-byte writes
> as valid page table writes. Any invalid GPA found is regarded as
> an error, either due to guest misbehavior/attack or bug in host
> shadow code.
> So,rather than do GFN pre-checking and replace invalid GFNs with
> scratch GFN and continue silently, just remove the pre-checking and
> abort PPGTT shadowing on error detected.
> c. GFN validity check is still performed in
> intel_gvt_dma_map_guest_page() --> gvt_pin_guest_page().
> It's more desirable to call VFIO interface to do both validity check
> and mapping.
> Calling intel_gvt_is_valid_gfn() to do GFN validity check from KVM side
> while later mapping the GFN through VFIO interface is unnecessarily
> fragile and confusing for unaware readers.
>
> Signed-off-by: Yan Zhao <[email protected]>
> [sean: remove now-unused local variables]
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> drivers/gpu/drm/i915/gvt/gtt.c | 36 +---------------------------------
> 1 file changed, 1 insertion(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 58b9b316ae46..f30922c55a0c 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -49,22 +49,6 @@
> static bool enable_out_of_sync = false;
> static int preallocated_oos_pages = 8192;
>
> -static bool intel_gvt_is_valid_gfn(struct intel_vgpu *vgpu, unsigned long gfn)
> -{
> - struct kvm *kvm = vgpu->vfio_device.kvm;
> - int idx;
> - bool ret;
> -
> - if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, vgpu->status))
> - return false;
> -
> - idx = srcu_read_lock(&kvm->srcu);
> - ret = kvm_is_visible_gfn(kvm, gfn);
> - srcu_read_unlock(&kvm->srcu, idx);
> -
> - return ret;
> -}
> -
> /*
> * validate a gm address and related range size,
> * translate it to host gm address
> @@ -1333,11 +1317,9 @@ static int ppgtt_populate_shadow_entry(struct intel_vgpu *vgpu,
> static int ppgtt_populate_spt(struct intel_vgpu_ppgtt_spt *spt)
> {
> struct intel_vgpu *vgpu = spt->vgpu;
> - struct intel_gvt *gvt = vgpu->gvt;
> - const struct intel_gvt_gtt_pte_ops *ops = gvt->gtt.pte_ops;
> struct intel_vgpu_ppgtt_spt *s;
> struct intel_gvt_gtt_entry se, ge;
> - unsigned long gfn, i;
> + unsigned long i;
> int ret;
>
> trace_spt_change(spt->vgpu->id, "born", spt,
> @@ -1354,13 +1336,6 @@ static int ppgtt_populate_spt(struct intel_vgpu_ppgtt_spt *spt)
> ppgtt_generate_shadow_entry(&se, s, &ge);
> ppgtt_set_shadow_entry(spt, &se, i);
> } else {
> - gfn = ops->get_pfn(&ge);
> - if (!intel_gvt_is_valid_gfn(vgpu, gfn)) {
> - ops->set_pfn(&se, gvt->gtt.scratch_mfn);
> - ppgtt_set_shadow_entry(spt, &se, i);
> - continue;
> - }
> -
> ret = ppgtt_populate_shadow_entry(vgpu, spt, i, &ge);
> if (ret)
> goto fail;
> @@ -2335,14 +2310,6 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
> m.val64 = e.val64;
> m.type = e.type;
>
> - /* one PTE update may be issued in multiple writes and the
> - * first write may not construct a valid gfn
> - */
> - if (!intel_gvt_is_valid_gfn(vgpu, gfn)) {
> - ops->set_pfn(&m, gvt->gtt.scratch_mfn);
> - goto out;
> - }
> -
> ret = intel_gvt_dma_map_guest_page(vgpu, gfn, PAGE_SIZE,
> &dma_addr);
> if (ret) {
> @@ -2359,7 +2326,6 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
> ops->clear_present(&m);
> }
>
> -out:
> ggtt_set_guest_entry(ggtt_mm, &e, g_gtt_index);
>
> ggtt_get_host_entry(ggtt_mm, &e, g_gtt_index);