Re: [PATCH] iommu/amd: Do not reallocate GA log buffers on resume

On Wed, Aug 19, 2026 at 05:23:49AM +0200, Karl Mehltretter wrote:
> Commit c5e1a1eb9279 ("iommu/amd: Simplify and Consolidate Virtual APIC
> (AVIC) Enablement") moved the GA log allocation from iommu_init_pci()
> to enable_iommus_vapic(), which is called on every resume.
> 
> iommu_init_ga_log() assigns iommu->ga_log and iommu->ga_log_tail
> unconditionally. Each resume therefore replaces the boot-time pointers
> and leaks both old allocations. The function also uses GFP_KERNEL from a
> syscore resume callback, where interrupts are disabled and the non-boot
> CPUs are offline.
> 
> Return early if both buffers are already allocated. Clear the pointers
> in free_ga_log() so a partial allocation failure cannot leave ga_log
> dangling.
> 
> Fixes: c5e1a1eb9279 ("iommu/amd: Simplify and Consolidate Virtual APIC (AVIC) Enablement")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Karl Mehltretter <[email protected]>

Reviewed-by: Ankit Soni <[email protected]>

Thanks,
Ankit

> ---
> Tested with custom QEMU with GA log emulation. Stock QEMU does not
> advertise GAMSup and cannot reach this path. After five pm_test=core
> cycles, nr_iommu_pages increased from 17 to 25 without the patch.
> 
> Testing on AVIC-capable hardware would be welcome.
> 
>  drivers/iommu/amd/init.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 40726dfef2733..c6b106d5921e 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -909,7 +909,9 @@ static void free_ga_log(struct amd_iommu *iommu)
>  {
>  #ifdef CONFIG_IRQ_REMAP
>  	iommu_free_pages(iommu->ga_log);
> +	iommu->ga_log = NULL;
>  	iommu_free_pages(iommu->ga_log_tail);
> +	iommu->ga_log_tail = NULL;
>  #endif
>  }
>  
> @@ -956,6 +958,9 @@ static int iommu_init_ga_log(struct amd_iommu *iommu)
>  	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
>  		return -EINVAL;
>  
> +	if (iommu->ga_log && iommu->ga_log_tail)
> +		return 0;
> +
>  	iommu->ga_log = iommu_alloc_pages_node_sz(nid, GFP_KERNEL, GA_LOG_SIZE);
>  	if (!iommu->ga_log)
>  		goto err_out;
> 
> base-commit: 4477a78374a57c3809b172ad30cceabda48c47c6
> -- 
> 2.53.0
>