On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
> @@ -242,8 +242,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> }
>
> old_pfn = gpc->pfn;
> - old_khva = gpc->khva - offset_in_page(gpc->khva);
> - old_uhva = gpc->uhva;
> + old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
>
> /* If the userspace HVA is invalid, refresh that first */
> if (gpc->gpa != gpa || gpc->generation != slots->generation ||
> @@ -259,13 +258,25 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> ret = -EFAULT;
> goto out;
> }
There's a subtle behaviour change here, isn't there? I'd *really* like
you do say 'No functional change intended' where that is true, and then
the absence of that sentence in this one would be meaningful.
You are now calling hva_to_pfn_retry() even when the uhva page hasn't
changed. Which is harmless and probably not important, but IIUC fixable
by the addition of:
+ if (gpc->uhva != PAGE_ALIGN_DOWN(old_uhva))
> + hva_change = true;
> + } else {
> + /*
> + * No need to do any re-mapping if the only thing that has
> + * changed is the page offset. Just page align it to allow the
> + * new offset to be added in.
> + */
> + gpc->uhva = PAGE_ALIGN_DOWN(gpc->uhva);
> }
>
> + /* Note: the offset must be correct before calling hva_to_pfn_retry() */
> + gpc->uhva += page_offset;
> +
> /*
> * If the userspace HVA changed or the PFN was already invalid,
> * drop the lock and do the HVA to PFN lookup again.
> */
> - if (!gpc->valid || old_uhva != gpc->uhva) {
> + if (!gpc->valid || hva_change) {
> ret = hva_to_pfn_retry(gpc);
> } else {
> /*
> --
But I don't really think it's that important if you can come up with a
coherent justification for the change and note it in the commit
message. So either way:
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
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