答复: [外部邮件] [PATCH 03/20] iommu/vt-d: Fix CACHE_TAG_NESTING_DEVTLB polluting shared variables in flush loop

[Li,Rongqing]

> From: Guanghui Feng <guanghuifeng@xxxxxxxxxxxxxxxxx>
> 
> In cache_tag_flush_range(), the CACHE_TAG_NESTING_DEVTLB case modifies the
> shared local variables 'addr' and 'mask' before falling through to
> CACHE_TAG_DEVTLB. This causes all subsequent CACHE_TAG_DEVTLB entries in
> the same loop iteration to incorrectly use the full-range flush parameters
> (addr=0, mask=MAX_AGAW_PFN_WIDTH) instead of the precisely calculated PSI
> range. This is not the intended behavior, as regular DEVTLB entries should always
> perform targeted range-based invalidation.
> 
> Fix this by having CACHE_TAG_NESTING_DEVTLB directly call
> cache_tag_flush_devtlb_psi() with the full-range constants and break, instead of
> modifying shared variables and falling through. This ensures
> CACHE_TAG_DEVTLB always uses the original calculated addr and mask for
> precise range flush.
> 
> Signed-off-by: Guanghui Feng <guanghuifeng@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guixin Liu <kanie@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/intel/cache.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/intel/cache.c b/drivers/iommu/intel/cache.c index
> fdc88817709f..26a758b0f501 100644
> --- a/drivers/iommu/intel/cache.c
> +++ b/drivers/iommu/intel/cache.c
> @@ -454,9 +454,8 @@ void cache_tag_flush_range(struct dmar_domain
> *domain, unsigned long start,
>  			 * affected by a change in S2. So just flush the entire
>  			 * device cache.
>  			 */
> -			addr = 0;
> -			mask = MAX_AGAW_PFN_WIDTH;
> -			fallthrough;
> +			cache_tag_flush_devtlb_psi(domain, tag, 0,
> MAX_AGAW_PFN_WIDTH);
> +			break;
>  		case CACHE_TAG_DEVTLB:
>  			cache_tag_flush_devtlb_psi(domain, tag, addr, mask);
>  			break;
> --
> 2.43.0

This patch introduces a subtle side effect on the tracing logic later in this function. 
At the end of cache_tag_flush_range(), trace_cache_tag_flush_range(tag, start, end, addr, mask) is called to log 
the flush operation. 

With this patch: bypassed the assignment and used break, addr and mask retain their original range values. 
This causes the tracepoint to log an incorrect, smaller range while the actual hardware execution was a full-range flush.

My patch has not this issue:
https://lore.kernel.org/linux-iommu/20260605003950.1720-1-lirongqing@xxxxxxxxx/

thanks

[Li,Rongqing]