linux-kernel - [RFC PATCH 1/1] powerpc/pseries/svm: Unshare all pages before kexecing a new kernel

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Message-Id: <20190607144703.GB8604@ram.ibm.com>
Date:   Fri, 7 Jun 2019 07:47:03 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        Ryan Grimm <grimm@...ux.vnet.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Subject: [RFC PATCH 1/1] powerpc/pseries/svm: Unshare all pages before
 kexecing a new kernel

powerpc/pseries/svm: Unshare all pages before kexecing a new kernel.
    
A new kernel deserves a clean slate. Any pages shared with the
hypervisor is unshared before invoking the new kernel. However there are
exceptions.  If the new kernel is invoked to dump the current kernel, or
if there is a explicit request to preserve the state of the current
kernel, unsharing of pages is skipped.
 
NOTE: Reserve atleast 256M for crashkernel.  Otherwise SWIOTLB
allocation fails and crash kernel fails to boot.
 
Signed-off-by: Ram Pai <linuxram@...ibm.com>

diff --git a/arch/powerpc/include/asm/ultravisor-api.h b/arch/powerpc/include/asm/ultravisor-api.h
index 8a6c5b4d..c8dd470 100644
--- a/arch/powerpc/include/asm/ultravisor-api.h
+++ b/arch/powerpc/include/asm/ultravisor-api.h
@@ -31,5 +31,6 @@
 #define UV_UNSHARE_PAGE			0xF134
 #define UV_PAGE_INVAL			0xF138
 #define UV_SVM_TERMINATE		0xF13C
+#define UV_UNSHARE_ALL_PAGES		0xF140
 
 #endif /* _ASM_POWERPC_ULTRAVISOR_API_H */
diff --git a/arch/powerpc/include/asm/ultravisor.h b/arch/powerpc/include/asm/ultravisor.h
index bf5ac05..73c44ff 100644
--- a/arch/powerpc/include/asm/ultravisor.h
+++ b/arch/powerpc/include/asm/ultravisor.h
@@ -120,6 +120,12 @@ static inline int uv_unshare_page(u64 pfn, u64 npages)
 	return ucall(UV_UNSHARE_PAGE, retbuf, pfn, npages);
 }
 
+static inline int uv_unshare_all_pages(void)
+{
+	unsigned long retbuf[UCALL_BUFSIZE];
+
+	return ucall(UV_UNSHARE_ALL_PAGES, retbuf);
+}
 #endif /* !__ASSEMBLY__ */
 
 #endif	/* _ASM_POWERPC_ULTRAVISOR_H */
diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index 75692c3..a93e3ab 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -329,6 +329,13 @@ void default_machine_kexec(struct kimage *image)
 #ifdef CONFIG_PPC_PSERIES
 	kexec_paca.lppaca_ptr = NULL;
 #endif
+
+	if (is_svm_platform() && !(image->preserve_context ||
+				   image->type == KEXEC_TYPE_CRASH)) {
+		uv_unshare_all_pages();
+		printk("kexec: Unshared all shared pages.\n");
+	}
+
 	paca_ptrs[kexec_paca.paca_index] = &kexec_paca;
 
 	setup_paca(&kexec_paca);