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Sashiko AI review found 3 potential issue(s) to consider: > - [High] iommu/amd: NULL pointer dereference in iommu_poll_ga_log() with GAPPI > - [Medium] iommu/amd: amd_iommu_gappi state inconsistent on VAPIC fallback > - [Low] iommu/amd: missing GAPPI in feat_str feature name array > -- > > commit f3f34d41f6c88bbaa635da8109c52cf22d09f580 > Author: Sairaj Kodilkar > > iommu/amd: Provide kernel command line option to enable GAPPI > > Enable GAPPI when the IOMMU GAPPISup extended feature bit is set and > the kernel is booted with the amd_iommu=gappi kernel parameter. > >> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h >> index b89a2b3df0a49..51edd617ddca2 100644 >> --- a/drivers/iommu/amd/amd_iommu_types.h >> +++ b/drivers/iommu/amd/amd_iommu_types.h >> @@ -78,6 +78,7 @@ >> #define FEATURE_X2APIC BIT_ULL(2) >> #define FEATURE_NX BIT_ULL(3) >> #define FEATURE_GT BIT_ULL(4) >> +#define FEATURE_GAPPI BIT_ULL(5) > > [Severity: Low] > This isn't a functional bug, but FEATURE_GAPPI is defined as bit 5. > > In print_iommu_info(), bit 5 is still hardcoded as "[5]" in the feature > string array: > > drivers/iommu/amd/init.c:print_iommu_info() { > ... > static const char * const feat_str[] = { > "PreF", "PPR", "X2APIC", "NX", "GT", "[5]", > "IA", "GA", "HE", "PC" > }; > ... > } > > Should "[5]" be updated to "GAPPI" so the kernel boot log displays the > correct feature name? > > [ ... ] >> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c >> index ef23e0755c32d..c536e0b3c4ff7 100644 >> --- a/drivers/iommu/amd/init.c >> +++ b/drivers/iommu/amd/init.c > [ ... ] >> @@ -3025,10 +3035,19 @@ static void enable_iommus_vapic(void) >> return; >> } >> >> + if (amd_iommu_gappi && >> + !(check_feature(FEATURE_GAPPI) && >> + AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))) { >> + pr_warn("GAPPI is not supported.\n"); >> + amd_iommu_gappi = false; >> + } > > [Severity: Medium] > If VAPIC is unsupported or disabled due to SNP, the code returns early just > above this diff and falls back to legacy mode: > > drivers/iommu/amd/init.c:enable_iommus_vapic() { > ... > if (!check_feature(FEATURE_GAM_VAPIC)) { > amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA; > return; > } > > if (amd_iommu_snp_en && > !FEATURE_SNPAVICSUP_GAM(amd_iommu_efr2)) { > pr_warn("Force to disable Virtual APIC due to SNP\n"); > amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA; > return; > } > ... > } > > These early returns bypass the new fallback check added here that sets > amd_iommu_gappi = false. > > If KVM subsequently reads the stale amd_iommu_gappi flag and attempts to set > up IRTE entries using GAPPI parameters, it calls irq_set_vcpu_affinity() > which triggers this check: > > drivers/iommu/amd/iommu.c:amd_ir_set_vcpu_affinity() { > ... > if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))) > return -EINVAL; > ... > } > > Could this result in a kernel warning and failure to configure the affinity > since the IOMMU driver actually fell back to legacy mode? > >> + >> /* Enabling GAM and SNPAVIC support */ >> for_each_iommu(iommu) { >> - if (iommu_init_ga_log(iommu) || >> - iommu_ga_log_enable(iommu)) >> + if (amd_iommu_gappi) >> + iommu_feature_enable(iommu, CONTROL_GAPPI_EN); >> + else if (iommu_init_ga_log(iommu) || >> + iommu_ga_log_enable(iommu)) >> return; > > [Severity: High] > If GAPPI is enabled, we skip allocating the GA log, so iommu->ga_log > remains NULL. > > If the previous kernel used the legacy GA log and left an interrupt pending, > or if an unmasked interrupt triggers the handler: > > drivers/iommu/amd/iommu.c:iommu_poll_ga_log() { > ... > head = readl(iommu->mmio_base + MMIO_GA_HEAD_OFFSET); > tail = readl(iommu->mmio_base + MMIO_GA_TAIL_OFFSET); > > while (head != tail) { > volatile u64 *raw; > ... > raw = (u64 *)(iommu->ga_log + head); > ... > /* Avoid memcpy function-call overhead */ > log_entry = *raw; > ... > } > > Won't the while loop unconditionally dereference iommu->ga_log which is now > NULL, crashing the kernel? > This is a valid concern. This is a pre-existing bug and can arise if second kernel has IRQ_REMAP disabled or fails to enable ga_log. Hence it is better to address this in a separate series. Thanks Sairaj