> -----Original Message-----
> From: Jan Kiszka
> Sent: dinsdag 24 augustus 2021 23:13
> On 02.02.21 17:44, Bram Hooimeijer wrote:
> > The procedures for shrinking and extending the cat_mask of the rool
> > cell affect other, non-root, cells as well, if these cell use the root COS.
> > That is, when cells are configured without cache regions. The code is
> > updated to reflect these changes not only in the root-cell, but in the
> > struct corresponding to these non-root cells as well.
> >
> > Fixes: 3f04eb1753bb ("x86: Introduce Cache Allocation Technology
> > support for Intel CPUs")
> >
> > Signed-off-by: Bram Hooimeijer
> > <[email protected]>
> > ---
> > hypervisor/arch/x86/cat.c | 31 +++++++++++++++++++++++++++----
> > 1 file changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/hypervisor/arch/x86/cat.c b/hypervisor/arch/x86/cat.c
> > index f6719b1e..42fd83d9 100644
> > --- a/hypervisor/arch/x86/cat.c
> > +++ b/hypervisor/arch/x86/cat.c
> > @@ -60,6 +60,13 @@ retry:
> > return cos;
> > }
> >
> > +/**
> > + * Merge available bits in the CBM back to root by modifying the
> > +cat_mask of
> > + * the root.
> > + *
> > + * It is the callers responsibility to call
> > +cat_update_cell(&root_cell), and
> > + * to modify the cat_mask of the non-root cells sharing the root's COS.
> > + */
> > static bool merge_freed_mask_to_root(void) {
> > bool updated = false;
> > @@ -86,6 +93,7 @@ static bool shrink_root_cell_mask(u64 cell_mask) {
> > unsigned int lo_mask_start, lo_mask_len;
> > u64 lo_mask;
> > + struct cell *cell;
> >
> > if ((root_cell.arch.cat_mask & ~cell_mask) == 0) {
> > /*
> > @@ -125,8 +133,17 @@ static bool shrink_root_cell_mask(u64 cell_mask)
> > }
> > }
> >
> > - printk("CAT: Shrunk root cell bitmask to %08llx\n",
> > - root_cell.arch.cat_mask);
> > + /* Cells using the root COS are also affected by shrinking. */
> > + printk("CAT: Set COS %d bitmask to %08llx for root cell",
> > + root_cell.arch.cos, root_cell.arch.cat_mask);
> > + for_each_non_root_cell(cell)
> > + if (cell->arch.cos == root_cell.arch.cos) {
> > + cell->arch.cat_mask = root_cell.arch.cat_mask;
> > + printk(", %s", cell->config->name);
> > + }
> > + printk("\n");
> > + /* However, updating the bitmask once suffices. This can be done
> > + * during code execution, no suspense required. (SDM 17.19.6.3)
> > + */
> > cat_update_cell(&root_cell);
> >
> > /* Drop this mask from the freed mask in case it was queued
> > there. */ @@ -201,8 +218,14 @@ static void cat_cell_exit(struct cell *cell)
> > freed_mask |= cell->arch.cat_mask & orig_root_mask;
> >
> > if (merge_freed_mask_to_root()) {
> > - printk("CAT: Extended root cell bitmask to %08llx\n",
> > - root_cell.arch.cat_mask);
> > + printk("CAT: Extended COS %d bitmask to %08llx for root cell",
> > + root_cell.arch.cos, root_cell.arch.cat_mask);
> > + for_each_non_root_cell(oth_cell)
> > + if (oth_cell->arch.cos == root_cell.arch.cos) {
> > + oth_cell->arch.cat_mask =
> > root_cell.arch.cat_mask;
> > + printk(", %s", cell->config->name);
> > + }
> > + printk("\n");
> > cat_update_cell(&root_cell);
> > }
> > }
> >
>
> Valid point that arch.cat_mask for the sharing cell gets out of sync.
> But what is the practical impact? We don't run cat_update_cell() for sharing
> cells, and cat_cell_exit() does nothing in that case. This is first of all to
> understand the impact of the issue.
Fair point. I am not 100% into the details anymore, but I guess you are right
that this does not have a practical impact. Of course, it can get a practical
impact in the future if someone decides to use the mask for something, so I
thought it would be good to fix it regardless.
>
> If there is impact, I'm considering to use (also) a mask pointer so that
> there is
> no need to walk all cells on root cell updates.
Just curious to get a better understanding of jailhouse: would these walks lead
to a performance hit? The other cells would not be preempted, right? So it is
just a list linear in the number of cells?
Thanks, Bram
>
> Jan
>
> --
> Siemens AG, T RDA IOT
> Corporate Competence Center Embedded Linux
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